Carbon monoxide inhalation ameliorates cold ischemia/reperfusion injury after rat liver transplantation

Carbon Monoxide Signaling: Examining Its Engagement with Various Molecular Targets in the Context of Binding Affinity, Concentration, and Biologic Response

Carbon monoxide (CO) has been firmly established as an endogenous signaling molecule with a variety of pathophysiological and pharmacological functions, including immunomodulation, organ protection, and circadian clock regulation, among many others. In terms of its molecular mechanism(s) of action, CO is known to bind to a large number of hemoproteins with at least 25 identified targets, including hemoglobin, myoglobin, neuroglobin, cytochrome c oxidase, cytochrome P450, soluble guanylyl cyclase, myeloperoxidase, and some ion channels with dissociation constant values spanning the range of sub-nM to high μM. Although CO's binding affinity with a large number of targets has been extensively studied and firmly established, there is a pressing need to incorporate such binding information into the analysis of CO's biologic response in the context of affinity and dosage. Especially important is to understand the reservoir role of hemoglobin in CO storage, transport, distribution, and transfer. We critically review the literature and inject a sense of quantitative assessment into our analyses of the various relationships among binding affinity, CO concentration, target occupancy level, and anticipated pharmacological actions. We hope that this review presents a picture of the overall landscape of CO's engagement with various targets, stimulates additional research, and helps to move the CO field in the direction of examining individual targets in the context of all of the targets and the concentration of available CO. We believe that such work will help the further understanding of the relationship of CO concentration and its pathophysiological functions and the eventual development of CO-based therapeutics. SIGNIFICANCE STATEMENT: The further development of carbon monoxide (CO) as a therapeutic agent will significantly rely on the understanding of CO's engagement with therapeutically relevant targets of varying affinity. This review critically examines the literature by quantitatively analyzing the intricate relationships among targets, target affinity for CO, CO level, and the affinity state of carboxyhemoglobin and provide a holistic approach to examining the molecular mechanism(s) of action for CO.

Retrospective evaluation of carboxyhemoglobin and methemoglobin levels in dogs and cats with respiratory disease

OBJECTIVE

To evaluate carboxyhemoglobin (COHb) and methemoglobin (MetHb) levels in dogs and cats with respiratory disease in the ICU.

DESIGN

Retrospective study.

SETTING

University veterinary teaching hospital.

ANIMALS

The ICU census was searched for dogs (n = 466) and cats (n = 97) hospitalized within the ICU between January 2016 and January 2019 in whom blood gas with co-oximetry was performed. Dogs and cats were stratified into those with primary respiratory and nonrespiratory categories; the underlying cause of the disease was also noted. Venous blood gas, co-oximeter, PaO₂ /FiO₂ (PF ratio), physical examination findings, and outcome were recorded.

MEASUREMENTS AND MAIN RESULTS

The median COHb and MetHb in dogs hospitalized in the ICU were 2.6% (0.1%-5.6%) and 1.1% (0.1%-2.9%), respectively. The median COHb and MetHb in cats hospitalized in the ICU were 2.2% (0.1%-5.4%) and 1.0% (0%-2.1%), respectively. Dogs with respiratory disease had a higher COHb than dogs without respiratory disease (median, 2.7% [range, 0.3%-5.0%] vs. 2.5% [0.1%-5.6%]; P = 0.0148). COHb was positively associated with survival in cats (median, 2.2% [range, 0.1%-5.4%] vs. 1.9% [0.1%-3.9%]; P = 0.0433). Both COHb and MetHb were higher in septic dogs than in nonseptic dogs (median COHb, 2.8% [range 0.3%-4.5%] vs. 2.6% [0.1%-5.6%]; P = 0.02 and median MetHb, 1.1% [0.1%-2.9%] vs. 1.1% [0.1%-2.4%]; P = 0.01, respectively).

CONCLUSIONS

There may be a positive association between COHb and respiratory disease in dogs; prospective studies are needed to evaluate this further. No association between COHb and respiratory disease in cats or MetHb and respiratory disease in either species was detected. Additional prospective studies are needed to determine whether COHb and MetHb are biomarkers for sepsis in dogs and whether COHb is an indicator of mortality in cats.

Carbon monoxide as an emerging pharmacological tool to improve lung and liver transplantation protocols

Carbon monoxide (CO) has long been considered purely as a toxic gas. It binds to hemoglobin at high concentrations and displaces oxygen from its binding site, resulting in carboxyhemoglobin formation, which reduces oxygen-carrying capacity of blood and culminates in tissue hypoxia and its associated complications. Recently, however, CO is quickly moving past its historic notorious tag as a poisonous gas to a physiological signaling molecule with therapeutic potentials in several clinical situations including transplant-induced injury. This review discusses current knowledge of CO gas and CO-releasing molecules (CO-RMs) in preclinical models of lung and liver transplantation, and underlying molecular mechanisms of cyto- and organ protection during organ procurement, preservation, implantation and post-transplant periods. In addition, a discussion of the future of CO in clinical organ transplantation is provided.

The potential relationship between gasotransmitters and oxidative stress, inflammation and apoptosis in lead-induced hepatotoxicity in rats

The interrelationship between gasotransmitters and oxidative stress, inflammation and apoptosis in lead-induced hepatotoxicity was investigated in this study. On prolonged exposure, lead was accumulated in liver tissue of rats and impaired liver function and structure as assessed by measurement of the serum hepatic function markers and by histopathological examination. The accumulated metal induced oxidative stress, inflammation and apoptosis in the liver. Also, it increased nitric oxide (NO) production and decreased hydrogen sulfide (H₂S) level and heme oxygenase (HO-1) concentration in liver tissue. Decreasing of NO production by L-N(G)-nitroarginine methyl ester (L-NAME) and increasing of H₂S level by sodium hydrosulfide (NaHS) and carbon monoxide (CO) level by carbon monoxide-releasing molecule-A₁ (CORM-A₁) inhibited lead-induced impairment of liver function and structure. Concomitantly, these agents inhibited lead intoxication-induced oxidative stress, inflammation, apoptosis, nitrosative stress and reduction of HO-1 concentration and H₂S level. Furthermore, concurrent treatment with these agents inhibited lead intoxication-induced increase in the protein expressions of inducible NO synthase, tumor necrosis factor-alpha, interleukin-1beta and caspase-3 as well as decrease in protein expressions of HO-1 and cystathionine-γ-lyase in the liver. NO donor, l-arginine and H₂S and CO biosynthesis inhibitors, trifluoro-DL-alanine and zinc deutroporphyrin, respectively aggravated the toxic effects of lead. These results indicate, for the first time, that there is an interrelationship between gasotransmitters and lead-induced hepatotoxicity. The ability of L-N AME, NaHS and CORM-A₁ to provide protective effects against lead-induced hepatotoxicity may positively correlate, to their ability to suppress hepatic oxidative stress, nitrosative stress, inflammation and apoptosis.

Isoglycyrrhizinate Magnesium Enhances Hepatoprotective Effect of FK506 on Ischemia-Reperfusion Injury Through HMGB1 Inhibition in a Rat Model of Liver Transplantation

BACKGROUND

Ischemia-reperfusion injury after liver transplantation (LT) impairs graft function and affects prognosis of recipients. Isoglycyrrhizinate magnesium (Iso) is a hepatoprotective drug usually used after liver injury. In this study, we intended to explore whether Iso alone have protective effect after ischemia-reperfusion injury in a rat model of liver transplantation. We also aimed to study whether Iso could enhance the hepatoprotective effect of FK506 (tacrolimus) and underlying mechanism.

METHODS

Rats after LT were treated with different concentration of FK506 with or without, Iso or lower-dose FK506 plus Iso. Alanine transaminase, aspartate transaminase, and albumin level were measured after 48 hours, 72 hours, and 7 days. A cell ischemic/reperfusion model was established to further study the mechanism of hepatoprotective effect of FK506 and Iso.

RESULTS

Iso treatment alone had no effect on liver grafts after LT, but lower-dose FK506 + Iso was better for maintenance of liver function than lower-dose FK506 alone at 48 hours, 72 hours, and 7 days after LT. In terms of mechanism, FK506 induced autophagy which resulted in significantly reduced apoptosis and maintained proliferative potential. However, autophagy induced by FK506 also lead to high-mobility group box (HMGB) 1 release from nuclei, resulting in hepatocyte injury through triggering of p38 phosphorylation and chemokine release. Iso effectively inhibited the release of HMGB1 and downstream inflammatory cytokines.

CONCLUSIONS

Iso could inhibit release of HMGB1 by FK506 and enhance the hepatoprotective effect of FK506 in rat LT. Combining Iso with FK506 would be promising for the patients after LT.

Carbon monoxide in lung cell physiology and disease

Carbon monoxide (CO) is an endogenously produced gas that has gained recognition as a biological signal transduction effector with properties similar, but not identical, to that of nitric oxide (NO). CO, which binds primarily to heme iron, may activate the hemoprotein guanylate cyclase, although with lower potency than NO. Furthermore, CO can modulate the activities of several cellular signaling molecules such as p38 MAPK, ERK1/2, JNK, Akt, NF-κB, and others. Emerging studies suggest that mitochondria, the energy-generating organelle of cells, represent a key target of CO action in eukaryotes. Dose-dependent modulation of mitochondrial function by CO can result in alteration of mitochondrial membrane potential, mitochondrial reactive oxygen species production, release of proapoptotic and proinflammatory mediators, as well as the inhibition of respiration at high concentration. CO, through modulation of signaling pathways, can impact key biological processes including autophagy, mitochondrial biogenesis, programmed cell death (apoptosis), cellular proliferation, inflammation, and innate immune responses. Inhaled CO is widely known as an inhalation hazard due to its rapid complexation with hemoglobin, resulting in impaired oxygen delivery to tissues and hypoxemia. Despite systemic and cellular toxicity at high concentrations, CO has demonstrated cyto- and tissue-protective effects at low concentration in animal models of organ injury and disease. These include models of acute lung injury (e.g., hyperoxia, hypoxia, ischemia-reperfusion, mechanical ventilation, bleomycin) and sepsis. The success of CO as a candidate therapeutic in preclinical models suggests potential clinical application in inflammatory and proliferative disorders, which is currently under evaluation in clinical trials.

Localized delivery of carbon monoxide

The heme oxygenase (HO)/carbon monoxide (CO) system is a physiological feedback loop orchestrating various cell-protective effects in response to cellular stress. The therapeutic use of CO is impeded by safety challenges as a result of high CO-Hemoglobin formation following non-targeted, systemic administration jeopardizing successful CO therapies as of this biological barrier. Another caveat is the use of CO-Releasing Molecules containing toxicologically critical transition metals. An emerging number of local delivery approaches addressing these issues have recently been introduced and provide exciting new starting points for translating the fascinating preclinical potential of CO into a clinical setting. This review will discuss these approaches and link to future delivery strategies aiming at establishing CO as a safe and effective medication of tomorrow.

The Protective Role of Carbon Monoxide (CO) Produced by Heme Oxygenases and Derived from the CO-Releasing Molecule CORM-2 in the Pathogenesis of Stress-Induced Gastric Lesions: Evidence for Non-Involvement of Nitric Oxide (NO)

Carbon monoxide (CO) produced by heme oxygenase (HO)-1 and HO-2 or released from the CO-donor, tricarbonyldichlororuthenium (II) dimer (CORM-2) causes vasodilation, with unknown efficacy against stress-induced gastric lesions. We studied whether pretreatment with CORM-2 (0.1-10 mg/kg oral gavage (i.g.)), RuCl₃ (1 mg/kg i.g.), zinc protoporphyrin IX (ZnPP) (10 mg/kg intraperitoneally (i.p.)), hemin (1-10 mg/kg i.g.) and CORM-2 (1 mg/kg i.g.) combined with N(G)-nitro-l-arginine (l-NNA, 20 mg/kg i.p.), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10 mg/kg i.p.), indomethacin (5 mg/kg i.p.), SC-560 (5 mg/kg i.g.), and celecoxib (10 mg/kg i.g.) affects gastric lesions following 3.5 h of water immersion and restraint stress (WRS). Gastric blood flow (GBF), the number of gastric lesions and gastric CO and nitric oxide (NO) contents, blood carboxyhemoglobin (COHb) level and the gastric expression of HO-1, HO-2, hypoxia inducible factor 1α (HIF-1α), tumor necrosis factor α (TNF-α), cyclooxygenase (COX)-2 and inducible NO synthase (iNOS) were determined. CORM-2 (1 mg/kg i.g.) and hemin (10 mg/kg i.g.) significantly decreased WRS lesions while increasing GBF, however, RuCl₃ was ineffective. The impact of CORM-2 was reversed by ZnPP, ODQ, indomethacin, SC-560 and celecoxib, but not by l-NNA. CORM-2 decreased NO and increased HO-1 expression and CO and COHb content, downregulated HIF-1α, as well as WRS-elevated COX-2 and iNOS mRNAs. Gastroprotection by CORM-2 and HO depends upon CO's hyperemic and anti-inflammatory properties, but is independent of NO.

Targeting heme oxygenase-1 and carbon monoxide for therapeutic modulation of inflammation

The heme oxygenase-1 (HO-1) enzyme system remains an attractive therapeutic target for the treatment of inflammatory conditions. HO-1, a cellular stress protein, serves a vital metabolic function as the rate-limiting step in the degradation of heme to generate carbon monoxide (CO), iron, and biliverdin-IXα (BV), the latter which is converted to bilirubin-IXα (BR). HO-1 may function as a pleiotropic regulator of inflammatory signaling programs through the generation of its biologically active end products, namely CO, BV and BR. CO, when applied exogenously, can affect apoptotic, proliferative, and inflammatory cellular programs. Specifically, CO can modulate the production of proinflammatory or anti-inflammatory cytokines and mediators. HO-1 and CO may also have immunomodulatory effects with respect to regulating the functions of antigen-presenting cells, dendritic cells, and regulatory T cells. Therapeutic strategies to modulate HO-1 in disease include the application of natural-inducing compounds and gene therapy approaches for the targeted genetic overexpression or knockdown of HO-1. Several compounds have been used therapeutically to inhibit HO activity, including competitive inhibitors of the metalloporphyrin series or noncompetitive isoform-selective derivatives of imidazole-dioxolanes. The end products of HO activity, CO, BV and BR may be used therapeutically as pharmacologic treatments. CO may be applied by inhalation or through the use of CO-releasing molecules. This review will discuss HO-1 as a therapeutic target in diseases involving inflammation, including lung and vascular injury, sepsis, ischemia-reperfusion injury, and transplant rejection.

5-Aminolevulinic acid regulates the inflammatory response and alloimmune reaction

5-Aminolevulinic acid (5-ALA) is a naturally occurring amino acid and precursor of heme and protoporphyrin IX (PpIX). Exogenously administrated 5-ALA increases the accumulation of PpIX in tumor cells specifically due to the compromised metabolism of 5-ALA to heme in mitochondria. PpIX emits red fluorescence by the irradiation of blue light and the formation of reactive oxygen species and singlet oxygen. Thus, performing a photodynamic diagnosis (PDD) and photodynamic therapy (PDT) using 5-ALA have given rise to a new strategy for tumor diagnosis and therapy. In addition to the field of tumor therapy, 5-ALA has been implicated in the treatment of inflammatory disease, autoimmune disease and transplantation due to the anti-inflammation and immunoregulation properties that are elicited with the expression of heme oxygenase (HO)-1, an inducible enzyme that catalyzes the rate-limiting step in the oxidative degradation of heme to free iron, biliverdin and carbon monoxide (CO), in combination with sodium ferrous citrate (SFC), because an inhibitor of HO-1 abolishes the effects of 5-ALA. Furthermore, NF-E2-related factor 2 (Nrf2), mitogen-activated protein kinase (MAPK), and heme are involved in the HO-1 expression. Biliverdin and CO are also known to have anti-apoptotic, anti-inflammatory and immunoregulatory functions. We herein review the current use of 5-ALA in inflammatory diseases, transplantation medicine, and tumor therapy.

Controlled therapeutic gas delivery systems for quality-improved transplants

Therapeutic gases enriched into perfusion solutions have been effectively used for the improvement of organ transplant quality. At present, the enrichment of perfusion solutions with gases requires complex machinery/containers and handling precautions. Alternatively, the gas is generated within the perfusion solution by supplemented carbonylated transition metal complexes with associated toxicological concerns when these metals contact the transplant. Therefore, we developed therapeutic gas releasing systems (TGRSs) allowing for the controlled generation and release of therapeutic gases (carbon monoxide and hydrogen sulfide) from otherwise hermetically sealed containers, such that the perfusion solution for the transplant is saturated with the gas but no other components from the TGRS are liberated in the solution. The release from the TGRS into the perfusion solution can be tailored as a function of the number and thickness of gas permeable membranes leading to release patterns having been linked to therapeutic success in previous trials. Furthermore, the surrogate biomarker HMGB1 was significantly downregulated in ischemic rat liver transplants perfused with enriched CO solution as compared to control. In conclusion, the TGRS allows for easy, reliable, and controlled generation and release of therapeutic gases while removing safety concerns of current approaches, thereby positively impacting the risk benefit profile of using therapeutic gases for transplant quality improvement in the future.

The therapeutic potential of carbon monoxide for inflammatory bowel disease

Inflammatory bowel disease (IBD), encompassing ulcerative colitis and Crohn's disease, are chronic, relapsing and remitting inflammatory disorders of the intestinal tract. Because the precise pathogenesis of IBD remains unclear, it is important to investigate the pathogenesis of IBD and to evaluate new anti-inflammatory strategies. Recent accumulating evidence has suggested that carbon monoxide (CO) may act as an endogenous defensive gaseous molecule to reduce inflammation and tissue injury in various organ injury models, including intestinal inflammation. Furthermore, exogenous CO administration at low concentrations is protective against intestinal inflammation. These data suggest that CO may be a novel therapeutic molecule in patients with IBD. In this review, we present what is currently known regarding the therapeutic potential of CO in intestinal inflammation.

Biliary tract external drainage increases the expression levels of heme oxygenase-1 in rat livers

BACKGROUND

Heme oxygenase-1 (HO-1) protects cells by anti-oxidation, maintaining normal microcirculation and anti-inflammatory under stress. This study investigated the effects of biliary tract external drainage (BTED) on the expression levels of HO-1 in rat livers.

METHODS

Biliary tract external drainage was performed by inserting a cannula into the bile duct. Sixty Sprague-Dawley rats were randomized to the following groups: sham 1 h group; BTED 1 h group; bile duct ligation (BDL) 1 h group; sham 6 h group and BTED 6 h group. The expression levels of HO-1 mRNA were analyzed using real-time RT-PCR. The expression levels of HO-1 were analyzed using immunohistochemistry.

RESULTS

The expression levels of HO-1 mRNA in the liver of the BTED group increased significantly compared with the sham group 1 and 6 h after surgery (p < 0.05).The expression levels of HO-1 in the BTED group increased significantly compared with the sham group 1 and 6 h after surgery. The expression levels of HO-1 mRNA in the liver in the BDL group decreased significantly compared with the sham group 1 h after surgery (p < 0.05).The expression levels of HO-1 in the BDL group decreased significantly compared with the sham group at this time.

CONCLUSION

Biliary tract external drainages increase the expression levels of HO-1 in the liver.

Carbon monoxide protects against hepatic ischemia/reperfusion injury by modulating the miR-34a/SIRT1 pathway

Hepatic ischemia/reperfusion (I/R) injury can arise as a complication of liver surgery and transplantation. Sirtuin 1 (SIRT1), an NAD+-dependent deacetylase, modulates inflammation and apoptosis in response to oxidative stress. SIRT1, which is regulated by p53 and microRNA-34a (miR-34a), can modulate non-alcoholic fatty liver disease, fibrosis and cirrhosis. Since carbon monoxide (CO) inhalation can protect against hepatic I/R, we hypothesized that CO could ameliorate hepatic I/R injury by regulating the miR-34a/SIRT1 pathway. Livers from mice pretreated with CO, or PFT, a p53 inhibitor, displayed reduced production of pro-inflammatory mediators, including TNF-α, iNOS, interleukin (IL)-6, and IL-1β after hepatic I/R injury. SIRT1 expression was increased by CO or PFT in the liver after I/R, whereas acetylated p65, p53 levels, and miR-34a expression were decreased. CO increased SIRT1 expression by inhibiting miR-34a. Both CO and PFT diminished pro-inflammatory cytokines production in vitro. Knockdown of SIRT1 in LPS-stimulated macrophages increased NF-κB acetylation, and increased pro-inflammatory cytokines. CO treatment reduced miR-34a expression and increased SIRT1 expression in oxidant-challenged hepatocytes; and rescued SIRT1 expression in p53-expressing or miR-34a transfected cells. In response to CO, enhanced SIRT1 expression mediated by miR-34a inhibition protects against liver damage through p65/p53 deacetylation, which may mediate inflammatory responses and hepatocellular apoptosis. The miR-34a/SIRT1 pathway may represent a therapeutic target for hepatic injury.

Ischemic preconditioning protects against liver ischemia/reperfusion injury via heme oxygenase-1-mediated autophagy

OBJECTIVES

Ischemic preconditioning exerts a protective effect in hepatic ischemia/reperfusion injury. The exact mechanism of ischemic preconditioning action remains largely unknown. Recent studies suggest that autophagy plays an important role in protecting against ischemia/reperfusion injury. However, the role of autophagy in ischemic preconditioning-afforded protection and its regulatory mechanisms in liver ischemia/reperfusion injury remain poorly understood. This study was designed to determine whether ischemic preconditioning could protect against liver ischemia/reperfusion injury via heme oxygenase-1-mediated autophagy.

DESIGN

Laboratory investigation.

SETTING

University animal research laboratory.

SUBJECTS

Male inbred Lewis rats and C57BL/6 mice.

INTERVENTIONS

Ischemic preconditioning was produced by 10 minutes of ischemia followed by 10 minutes of reperfusion prior to 60 minutes of ischemia. In a rat model of hepatic ischemia/reperfusion injury, rats were pretreated with wortmannin or rapamycin to evaluate the contribution of autophagy to the protective effects of ischemic preconditioning. Heme oxygenase-1 was inhibited with tin protoporphyrin IX. In a mouse model of hepatic ischemia/reperfusion injury, autophagy or heme oxygenase-1 was inhibited with vacuolar protein sorting 34 small interfering RNA or heme oxygenase-1 small interfering RNA, respectively.

MEASUREMENTS AND MAIN RESULTS

Ischemic preconditioning ameliorated liver ischemia/reperfusion injury, as indicated by lower serum aminotransferase levels, lower hepatic inflammatory cytokines, and less severe ischemia/reperfusion-associated histopathologic changes. Ischemic preconditioning treatment induced autophagy activation, as indicated by an increase of LC3-II, degradation of p62, and accumulation of autophagic vacuoles in response to ischemia/reperfusion injury. When ischemic preconditioning-induced autophagy was inhibited with wortmannin in rats or vacuolar protein sorting 34-specific small interfering RNA in mice, liver ischemia/reperfusion injury was worsened, whereas rapamycin treatment increased autophagy and mimicked the protective effects of ischemic preconditioning. Furthermore, ischemic preconditioning increased heme oxygenase-1 expression. The inhibition of heme oxygenase-1 with tin protoporphyrin IX in rats or heme oxygenase-1-specific small interfering RNA in mice decreased ischemic preconditioning-induced autophagy and diminished the protective effects of ischemic preconditioning against ischemia/reperfusion injury.

CONCLUSIONS

Ischemic preconditioning protects against liver ischemia/reperfusion injury, at least in part, via heme oxygenase-1-mediated autophagy.

The CO donor CORM-2 inhibits LPS-induced vascular cell adhesion molecule-1 expression and leukocyte adhesion in human rheumatoid synovial fibroblasts

BACKGROUND AND PURPOSE

Infection with Gram-negative bacteria has been recognized as an initiator of rheumatoid arthritis, which is characterized by chronic inflammation and infiltration of immune cells. Carbon monoxide (CO) exhibits anti-inflammatory properties. Here we have investigated the detailed mechanisms of vascular cell adhesion molecule-1 (VCAM-1) expression induced by LPS and if CO inhibited LPS-induced leukocyte adhesion to synovial fibroblasts by suppressing VCAM-1 expression.

EXPERIMENTAL APPROACH

Human rheumatoid arthritis synovial fibroblasts (RASFs) were incubated with LPS and/or the CO-releasing compound CORM-2. Effects of LPS on VCAM-1 levels were determined by analysing mRNA expression, promoter activity, protein expression, and immunohistochemical staining. The molecular mechanisms were investigated by determining the expression, activation, and binding activity of transcriptional factors using target signal antagonists.

KEY RESULTS

CORM-2 significantly inhibited inflammatory responses in LPS-treated RASFs by down-regulating the expression of adhesion molecule VCAM-1 and leukocyte infiltration. The down-regulation of LPS-induced VCAM-1 expression involved inhibition of the expression of phosphorylated-NF-κB p65 and AP-1 (p-c-Jun, c-Jun and c-Fos mRNA levels). These results were confirmed by chromatin immunoprecipitation assay to detect NF-κB and AP-1 DNA binding activity.

CONCLUSIONS AND IMPLICATIONS

LPS-mediated formation of the TLR4/MyD88/TRAF6/c-Src complex regulated NF-κB and MAPKs/AP-1 activation leading to VCAM-1 expression and leukocyte adhesion. CORM-2, which liberates CO to elicit direct biological activities, attenuated LPS-induced VCAM-1 expression by interfering with NF-κB and AP-1 activation, and significantly reduced LPS-induced immune cell infiltration of the synovium.

Carbon monoxide protects against hepatic ischemia/reperfusion injury via ROS-dependent Akt signaling and inhibition of glycogen synthase kinase 3β

Carbon monoxide (CO) may exert important roles in physiological and pathophysiological states through the regulation of cellular signaling pathways. CO can protect organ tissues from ischemia/reperfusion (I/R) injury by modulating intracellular redox status and by inhibiting inflammatory, apoptotic, and proliferative responses. However, the cellular mechanisms underlying the protective effects of CO in organ I/R injury remain incompletely understood. In this study, a murine model of hepatic warm I/R injury was employed to assess the role of glycogen synthase kinase-3 (GSK3) and phosphatidylinositol 3-kinase (PI3K)-dependent signaling pathways in the protective effects of CO against inflammation and injury. Inhibition of GSK3 through the PI3K/Akt pathway played a crucial role in CO-mediated protection. CO treatment increased the phosphorylation of Akt and GSK3-beta (GSK3β) in the liver after I/R injury. Furthermore, administration of LY294002, an inhibitor of PI3K, compromised the protective effect of CO and decreased the level of phospho-GSK3β after I/R injury. These results suggest that CO protects against liver damage by maintaining GSK3β phosphorylation, which may be mediated by the PI3K/Akt signaling pathway. Our study provides additional support for the therapeutic potential of CO in organ injury and identifies GSK3β as a therapeutic target for CO in the amelioration of hepatic injury.

Therapeutic applications of carbon monoxide

Heme oxygenase-1 (HO-1) is a regulated enzyme induced in multiple stress states. Carbon monoxide (CO) is a product of HO catalysis of heme. In many circumstances, CO appears to functionally replace HO-1, and CO is known to have endogenous anti-inflammatory, anti-apoptotic, and antiproliferative effects. CO is well studied in anoxia-reoxygenation and ischemia-reperfusion models and has advanced to phase II trials for treatment of several clinical entities. In alternative injury models, laboratories have used sepsis, acute lung injury, and systemic inflammatory challenges to assess the ability of CO to rescue cells, organs, and organisms. Hopefully, the research supporting the protective effects of CO in animal models will translate into therapeutic benefits for patients. Preclinical studies of CO are now moving towards more complex damage models that reflect polymicrobial sepsis or two-step injuries, such as sepsis complicated by acute respiratory distress syndrome. Furthermore, co-treatment and post-treatment with CO are being explored in which the insult occurs before there is an opportunity to intervene therapeutically. The aim of this review is to discuss the potential therapeutic implications of CO with a focus on lung injury and sepsis-related models.

5-Aminolevulinic acid combined with ferrous iron induces carbon monoxide generation in mouse kidneys and protects from renal ischemia-reperfusion injury

Renal ischemia reperfusion injury (IRI) is a major factor responsible for acute renal failure. An intermediate in heme synthesis, 5-aminolevulinic acid (5-ALA) is fundamental in aerobic energy metabolism. Heme oxygenase (HO)-1 cleaves heme to form biliverdin, carbon monoxide (CO), and iron (Fe(2+)), which is used with 5-ALA. In the present study, we investigated the role of 5-ALA in the attenuation of acute renal IRI using a mouse model. Male Balb/c mice received 30 mg/kg 5-ALA with Fe(2+) 48, 24, and 2 h before IRI and were subsequently subjected to bilateral renal pedicle occlusion for 45 min. The endogenous CO concentration of the kidneys from the mice administered 5-ALA/Fe(2+) increased significantly, and the peak concentrations of serum creatinine and blood urea nitrogen decreased. 5-ALA/Fe(2+) treatments significantly decreased the tubular damage and number of apoptotic cells. IRI-induced renal thiobarbituric acid-reactive substance levels were also significantly decreased in the 5-ALA/Fe(2+) group. Furthermore, mRNA expression of HO-1, TNF-α, and interferon-γ was significantly increased after IRI. Levels of HO-1 were increased and levels of TNF-α and interferon-γ were decreased in the 5-ALA/Fe(2+)-pretreated renal parenchyma after IRI. F4/80 staining showed reduced macrophage infiltration, and TUNEL staining revealed that there were fewer interstitial apoptotic cells. These findings suggest that 5-ALA/Fe(2+) can protect the kidneys against IRI by reducing macrophage infiltration and decreasing renal cell apoptosis via the generation of CO.

Carbon monoxide: present and future indications for a medical gas

Gaseous molecules continue to hold new promise in molecular medicine as experimental and clinical therapeutics. The low molecular weight gas carbon monoxide (CO), and similar gaseous molecules (e.g., H2S, nitric oxide) have been implicated as potential inhalation therapies in inflammatory diseases. At high concentration, CO represents a toxic inhalation hazard, and is a common component of air pollution. CO is also produced endogenously as a product of heme degradation catalyzed by heme oxygenase enzymes. CO binds avidly to hemoglobin, causing hypoxemia and decreased oxygen delivery to tissues at high concentrations. At physiological concentrations, CO may have endogenous roles as a signal transduction molecule in the regulation of neural and vascular function and cellular homeostasis. CO has been demonstrated to act as an effective anti-inflammatory agent in preclinical animal models of inflammation, acute lung injury, sepsis, ischemia/reperfusion injury, and organ transplantation. Additional experimental indications for this gas include pulmonary fibrosis, pulmonary hypertension, metabolic diseases, and preeclampsia. The development of chemical CO releasing compounds constitutes a novel pharmaceutical approach to CO delivery with demonstrated effectiveness in sepsis models. Current and pending clinical evaluation will determine the usefulness of this gas as a therapeutic in human disease.

Carbon monoxide in exhaled breath testing and therapeutics

Carbon monoxide (CO), a low molecular weight gas, is a ubiquitous environmental product of organic combustion, which is also produced endogenously in the body, as the byproduct of heme metabolism. CO binds to hemoglobin, resulting in decreased oxygen delivery to bodily tissues at toxicological concentrations. At physiological concentrations, CO may have endogenous roles as a potential signaling mediator in vascular function and cellular homeostasis. Exhaled CO (eCO), similar to exhaled nitric oxide (eNO), has been evaluated as a candidate breath biomarker of pathophysiological states, including smoking status, and inflammatory diseases of the lung and other organs. eCO values have been evaluated as potential indicators of inflammation in asthma, stable COPD and exacerbations, cystic fibrosis, lung cancer, or during surgery or critical care. The utility of eCO as a marker of inflammation and its potential diagnostic value remain incompletely characterized. Among other candidate 'medicinal gases' with therapeutic potential, (e.g., NO and H2S), CO has been shown to act as an effective anti-inflammatory agent in preclinical animal models of inflammatory disease, acute lung injury, sepsis, ischemia/reperfusion injury and organ graft rejection. Current and future clinical trials will evaluate the clinical applicability of this gas as a biomarker and/or therapeutic in human disease.

The immunomodulatory role of carbon monoxide during transplantation

The number of organ and tissue transplants has increased worldwide in recent decades. However, graft rejection, infections due to the use of immunosuppressive drugs and a shortage of graft donors remain major concerns. Carbon monoxide (CO) had long been regarded solely as a poisonous gas. Ultimately, physiological studies unveiled the endogenous production of CO, particularly by the heme oxygenase (HO)-1 enzyme, recognizing CO as a beneficial gas when used at therapeutic doses. The protective properties of CO led researchers to develop uses for it, resulting in devices and molecules that can deliver CO in vitro and in vivo. The resulting interest in clinical investigations was immediate. Studies regarding the CO/HO-1 modulation of immune responses and their effects on various immune disorders gave rise to transplantation research, where CO was shown to be essential in the protection against organ rejection in animal models. This review provides a perspective of how CO modulates the immune system to improve transplantation and suggests its use as a therapy in the field.

Treprostinil Improves Hepatic Cytochrome P450 Activity during Rat Liver Transplantation

BACKGROUND

Cytochrome P450 (CYP450) activity is an important indicator of liver graft function. CYP450 activity is altered by pro-inflammatory cytokines, which are associated with ischemia-reperfusion (I/R) injury during orthotopic liver transplantation (OLT). Treprostinil, an FDA-approved prostacyclin analog, ameliorated cold I/R injury during rat OLT. We hypothesized that treprostinil would improve CYP450 activity in liver graft during cold I/R injury post-OLT.

METHODS

OLT was performed in syngeneic male Lewis rats with 18 h graft preservation in cold UW solution. Donor and recipients received treprostinil (100 ng/kg/min) or matching placebo for 24 h before and up to 48 h post-OLT. Liver graft mRNA and protein expression of CYP450 isoforms were analyzed by qRT-PCR and Western blot analysis, respectively. The formation rates of 1-hydroxymidazolam and 6β-hydroxytestosterone, 6-hydroxychlorzoxazone, 2α- and 16α-hydroxytestosterone in liver graft microsomes served as markers for CYP3A, CYP2E1, and CYP2C11 activity, respectively, and were measured by LC-MS.

RESULTS

Treprostinil significantly decreased serum ALT and AST levels at 6-48 h after OLT, compared to placebo. The expressions of TNFα and IFNγ mRNA in the liver graft were significantly inhibited in the treprostinil-treated group at 1 h post-reperfusion. Treprostinil restored CYP2E1 protein expression to that of normal liver and significantly improved CYP3A activity to more than two-fold of placebo early post-OLT.

CONCLUSIONS

Treprostinil significantly ameliorated hepatic injury, reduced expression of pro-inflammatory cytokines, and improved CYP450 activity in liver graft early post-OLT. These findings suggest that treprostinil has the potential to serve as a therapeutic option to protect liver graft function against I/R injury during clinical OLT.

Nitrite reduces acute lung injury and improves survival in a rat lung transplantation model

Ischemia/reperfusion injury (IRI) is the most common cause of early mortality following lung transplantation (LTx). We hypothesized that nitrite, an endogenous source of nitric oxide (NO), may protect lung grafts from IRI. Rat lung grafts were stored in preservation solution at 4°C for 6 hours. Both grafts and recipients were treated with nitrite. Nitrite treatment was associated with significantly higher levels of tissue oxygenation, lower levels of cytokines and neutrophil/macrophage infiltration, lower myeloperoxidase activity, reduced oxidative injury and increased cGMP levels in grafts than in the controls. Treatment with either a nitric oxide scavenger or a soluble guanylyl cyclase (sGC) inhibitor diminished the beneficial effects of nitrite and decreased cGMP concentrations. These results suggest that nitric oxide, generated from nitrite, is the molecule responsible for the effects of nitrite via the nitric oxide/sGC/cGMP pathway. Allopurinol, a xanthine oxidoreductase (XOR) inhibitor, abrogated the protective effects of nitrite, suggesting that XOR is a key enzyme in the conversion of nitrite to nitric oxide. In vitro experiments demonstrated that nitrite prevented apoptosis in pulmonary endothelial cells. Nitrite also exhibits longer survival rate in recipients than control. In conclusion, nitrite inhibits lung IRI following cold preservation and had higher survival rate in LTx model.

Inhalation of hydrogen gas reduces liver injury during major hepatotectomy in swine

AIM: To study the effect of H₂ gas on liver injury in massive hepatectomy using the Intermittent Pringle maneuver in swine.

METHODS: Male Bama pigs (n = 14) treated with ketamine hydrochloride and Sumianxin II as induction drugs followed by inhalation anesthesia with 2% isoflurane, underwent 70% hepatotectomy with loss of bleeding less than 50 mL, and with hepatic pedicle occlusion for 20 min, were divided into two groups: Hydrogen-group (n = 7), the pigs with inhalation of 2% hydrogen by the tracheal intubation during major hepatotectomy; Contrast-group (n = 7), underwent 70% hepatotectomy without inhalation of hydrogen. Hemodynamic changes and plasma concentrations of alanine aminotransferase (ALT), aspartate aminotransferase (AST), hyaluronic acid (HA), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and malondialdehyde (MDA) in liver tissue were measured at pre-operation, post-hepatotectomy (PH) 1 h and 3 h. The apoptosis and proliferating cell nuclear antigen (PCNA) expression in liver remnant were evaluated at PH 3 h. Then we compared the two groups by these marks to evaluate the effect of the hydrogen in the liver injury during major hepatotectomy with the Pringle Maneuver in the swine.

RESULTS: There were no significant differences in body weight, blood loss and removal liver weight between the two groups. There was no significant difference in changes of portal vein pressure between two groups at pre-operation, PH 30 min, but in hydrogen gas treated-group it slightly decrease and lower than its in Contrast-group at PH 3 h, although there were no significant difference (P = 0.655). ALT and AST in Hydrogen-group was significantly lower comparing to Contrast-group (P = 0.036, P = 0.011, vs P = 0.032, P = 0.013) at PH 1 h and 3 h, although the two groups all increased. The MDA level increased between the two group at PH 1 h and 3 h. In the hydrogen gas treated-group, the MDA level was not significantly significant at pre-operation and significantly low at PH 1 h and 3 h comparing to Contrast-group (P = 0.0005, P = 0.0004). In Hydrogen-group, the HA level was also significantly low to Contrast-group (P = 0.0005, P = 0.0005) although the two groups all increased at PH 1 h and 3 h. The expression of cluster of differentiation molecule 31 molecules Hydrogen-group was low to Contrast-group. However, PCNA index (%) was not statistically significant between the two groups (P = 0.802). Microphotometric evaluation of apoptotic index (AI) in terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling-stained tissue after hepatotectomy for 3h, the AI% level in the hydrogen was significantly low to Contrast-group (P = 0.012). There were no significant difference between Hydrogen-group and Contrast-group at pre-operation (P = 0.653, P = 0.423), but after massive hepatotectomy, the TNF-α and IL-6 levels increase, and its in Hydrogen-group was significantly low compared with Contrast-group (P = 0.022, P = 0.013, vs P = 0.016, P = 0.012), respectively. Hydrogen-gas inhalation reduce levels of these markers and relieved morphological liver injury and apoptosis.

CONCLUSION: H₂ gas attenuates markedly ischemia and portal hyperperfusion injury in pigs with massive hepatotectomy, possibly by the reduction of inflammation and oxidative stress, maybe a potential agent for treatment in clinic.

Colonic insufflation with carbon monoxide gas inhibits the development of intestinal inflammation in rats

Background

The pathogenesis of inflammatory bowel disease (IBD) is complex, and an effective therapeutic strategy has yet to be established. Recently, carbon monoxide (CO) has been reported to be capable of reducing inflammation by multiple mechanisms. In this study, we evaluated the role of colonic CO insufflation in acute colitis induced by trinitrobenzene sulfonic acid (TNBS) in rats.

Methods

Acute colitis was induced with TNBS in male Wistar rats. Following TNBS administration, the animals were treated daily with 200 ppm of intrarectal CO gas. The distal colon was removed to evaluate various parameters of inflammation, including thiobarbituric acid (TBA)-reactive substances, tissue-associated myeloperoxidase (MPO) activity, and the expression of cytokine-induced neutrophil chemoattractant (CINC)-1 in colonic mucosa 7 days after TNBS administration.

Results

The administration of TNBS induced ulceration with surrounding edematous swelling in the colon. In rats treated with CO gas, the colonic ulcer area was smaller than that of air-treated rats 7 days after TNBS administration. The wet colon weight was significantly increased in the TNBS-induced colitis group, which was markedly abrogated by colonic insufflation with CO gas. The increase of MPO activity, TBA-reactive substances, and CINC-1 expression in colonic mucosa were also significantly inhibited by colonic insufflation with CO gas.

Conclusions

Colonic insufflation with CO gas significantly ameliorated TNBS-induced colitis in rats. Clinical application of CO gas to improve colonic inflammatory conditions such as IBD might be useful.

Kinetic effects of carbon monoxide inhalation on tissue protection in ventilator-induced lung injury

Mechanical ventilation causes ventilator-induced lung injury (VILI), and contributes to acute lung injury/acute respiratory distress syndrome (ALI/ARDS), a disease with high morbidity and mortality among critically ill patients. Carbon monoxide (CO) can confer lung protective effects during mechanical ventilation. This study investigates the time dependency of CO therapy with respect to lung protection in animals subjected to mechanical ventilation. For this purpose, mice were ventilated with a tidal volume of 12 ml/kg body weight for 6 h with air in the absence or presence of CO (250 parts per million). Histological analysis of lung tissue sections was used to determine alveolar wall thickening and the degree of lung damage by VILI score. Bronchoalveolar lavage fluid was analyzed for total cellular influx, neutrophil accumulation, and interleukin-1β release. As the main results, mechanical ventilation induced pulmonary edema, cytokine release, and neutrophil recruitment. In contrast, application of CO for 6 h prevented VILI. Although CO application for 3 h followed by 3-h air ventilation failed to prevent lung injury, a further reduction of CO application time to 1 h in this setting provided sufficient protection. Pre-treatment of animals with inhaled CO for 1 h before ventilation showed no beneficial effect. Delayed application of CO beginning at 3 or 5 h after initiation of ventilation, reduced lung damage, total cell influx, and neutrophil accumulation. In conclusion, administration of CO for 6 h protected against VILI. Identical protective effects were achieved by limiting the administration of CO to the first hour of ventilation. Pre-treatment with CO had no impact on VILI. In contrast, delayed application of CO led to anti-inflammatory effects with time-dependent reduction in tissue protection.

Contributions of heme oxygenase-1 in postconditioning-protected ischemia-reperfusion injury in rat liver transplantation

BACKGROUND

Heme oxygenase-1 (HO-1), an oxidative stress-response gene up-regulated by various physiological and exogenous stimuli, has cytoprotective activities. Ischemic postconditioning (Postcon) can protect an organ from ischemia-reperfusion (I/R) injury. In the present study, we investigated the potential contributions of HO-1 to Postcon-dependent protection against I/R injury in rat liver transplantation models.

MATERIALS AND METHODS

Adult male Sprague-Dawley rats were randomly divided into four groups: sham group with laparotomy for liver exposure; I/R group with 24-hour cold ischemia of the donor liver; Postcon group with the same treatment as the I/R group plus ischemic Postcon; and zinc protoporphyrin (ZnPP HO-1 inhibitor) + Postcon group treated the same as the Postcon cohort with donors pretreated using ZnPP 24 hours before the I/R injury. We measured liver tissue and peripheral blood samples collected at 6 hours after reperfusion and serum transaminase levels, histopathology, liver tissue malondialdehyde (MDA) content, superoxide dismutase (SOD) activity and HO-1 expression in the liver.

RESULTS

Postcon significantly diminished the elevation of serum transaminases levels after I/R injury when compared with I/R and ZnPP+Postcon groups. Postcon treated rats showed significantly lower MDA production and higher SOD activity. HO-1 was induced in rat livers exposed to Postcon; its levels were obviously overexpressed after 6 hours in Postcon rats. Inhibiting the expression of HO-1, negated the protective effects of Postcon.

CONCLUSIONS

Induction of HO-1 in the Postcon condition played a protective role against hepatic I/R injury and enhanced the early antioxidative activity. The protective effects of Postcon were significantly associated with greater intrahepatic HO-1 expression.

Carbon monoxide induces hypothermia tolerance in Kupffer cells and attenuates liver ischemia/reperfusion injury in rats

Ischemia/reperfusion (I/R) injury in liver grafts, which is initiated by cold preservation and is augmented by reperfusion, is a major problem that complicates graft quality, posttransplant patient care, and outcomes of liver transplantation (LT). Kupffer cells (KCs) play important roles in I/R injury; however, little is known about their changes during cold preservation. We examined whether a pretreatment with carbon monoxide (CO), a cytoprotective product of heme degradation, could influence KC activity during cold storage and protect liver grafts against LT-induced I/R injury. In vitro, primary rat KCs were stimulated for 24 hours under hypothermic conditions (4°C, 20% O(2)), with lipopolysaccharide, or under hypoxic conditions (37°C, 5% O(2)) with or without a CO pretreatment. When rat KCs were exposed to hypothermic conditions, they produced reactive oxygen species (ROS), but they did not produce tumor necrosis factor α (TNF-α) or nitric oxide. The preincubation of KCs with CO up-regulated heat shock protein 70 (HSP70) and inhibited ROS generation. When liver grafts from donor rats exposed to CO (250 ppm) for 24 hours were transplanted after 18 hours of cold preservation in University of Wisconsin solution, HSP70 expression increased in these grafts versus control grafts, and serum aspartate aminotransferase and alanine aminotransferase levels as well as necrotic areas and inflammatory infiltrates were significantly reduced after LT. CO-pretreated liver grafts showed less up-regulation of TNF-α and inducible nitric oxide synthase messenger RNA (mRNA) and reduced expression of proapoptotic B cell lymphoma 2-associated X protein mRNA, cleaved caspase-3, and poly(adenosine diphosphate ribose) polymerase. In conclusion, the pretreatment of donors with CO ameliorates LT-associated I/R injury with increased hepatic HSP70 expression, particularly in the KC population.

Use of carbon monoxide in minimizing ischemia/reperfusion injury in transplantation

Although carbon monoxide (CO) is known to be toxic because of its ability to interfere with oxygen delivery at high concentrations, mammalian cells endogenously generate CO primarily via the catalysis of heme by heme oxygenases. Recent findings have indicated that heme oxygenases and generation of CO serve as a key mechanism to maintain the integrity of the physiological function of organs and supported the development of a new paradigm that CO, at low concentrations, functions as a signaling molecule in the body and exerts significant cytoprotection. Consequently, exogenously delivered CO has been shown to mediate potent protection in various injury models through its anti-inflammatory, vasodilating, and antiapoptotic functions. Ischemia/reperfusion (I/R) injury associated with organ transplantation is one of the major deleterious factors limiting the success of transplantation. Ischemia/reperfusion injury is a complex cascade of interconnected events involving cell damage, apoptosis, vigorous inflammatory responses, microcirculation disturbance, and thrombogenesis. Carbon monoxide has a great potential in minimizing I/R injury. This review will provide an overview of the basic physiology of CO, preclinical studies examining efficacy of CO in I/R injury models, and possible protective mechanisms. Carbon monoxide could be developed to be a valuable therapeutic molecule in minimizing I/R injury in transplantation.

The role of heme oxygenase and carbon monoxide in inflammatory bowel disease

Inflammatory bowel disease (IBD), including ulcerative colitis (UC) and Crohn's disease, is a chronic and recurrent inflammatory disorder of the intestinal tract. Since the precise pathogenesis of IBD remains unclear, it is important to investigate the pathogenesis of IBD and to evaluate new anti-inflammatory strategies. Recent evidence suggests that heme oxygenase-1 (HO-1) plays a critical protective role during the development of intestinal inflammation. In fact, it has been demonstrated that the activation of HO-1 may act as an endogenous defensive mechanism to reduce inflammation and tissue injury in various animal intestinal injury models induced by ischemia-reperfusion, indomethacin, lipopolysaccharide-associated sepsis, trinitrobenzene sulfonic acid or dextran sulfate sodium. In addition, carbon monoxide (CO) derived from HO-1 has been shown to be involved in the regulation of intestinal inflammation. Furthermore, administration of a low concentration of exogenous CO has a protective effect against intestinal inflammation. These data suggest that HO-1 and CO may be novel therapeutic molecules for patients with gastrointestinal inflammatory diseases. In this review, we present what is currently known regarding the role of HO-1 and CO in intestinal inflammation.

Inhalation of carbon monoxide ameliorates TNBS-induced colitis in mice through the inhibition of TNF-α expression

BACKGROUND

Carbon monoxide (CO), long considered a toxic gas, has recently been shown to mediate anti-inflammatory effects in various animal models. The aim of this study was to investigate whether the inhalation of CO ameliorated 2,4,6-trinitrobenzine sulfonic acid (TNBS)-induced colitis in mice.

METHODS

The CO treatment group was exposed to CO gas at a concentration of 200 ppm in a closed cage starting on the day when TNBS was administered and throughout the remaining study period. The distal colon was removed, and ulcerative lesions were subsequently evaluated with macroscopic damage scores. Furthermore, thiobarbituric acid (TBA)-reactive substances and tissue-associated myeloperoxidase (MPO) activity in colonic mucosa were measured as indices of lipid peroxidation and neutrophil infiltration. The expressions of TNF-α in colonic mucosa were also measured by enzyme-linked immunosorbent assay. In additional experiments in vitro, CD4(+) T cells isolated from the spleen were stimulated with anti-CD3/CD28 Ab, and the cells and supernatants were collected and evaluated for TNF-α expression.

RESULTS

The increased colonic damage after TNBS administration was significantly inhibited by the treatment with CO. Furthermore, CO significantly inhibited the increases in TBA-reactive substances, MPO activity and TNF-α production in colonic mucosa after the induction of TNBS colitis. In CD4(+) T cells isolated from mice treated with CO inhalation, the production of TNF-α was significantly inhibited.

CONCLUSIONS

The inhalation of CO protected mice from developing intestinal inflammation. Based on these data, the beneficial effects of CO in a murine colitis model may be attributed to its anti-inflammatory properties.

Molecular biology of liver ischemia/reperfusion injury: established mechanisms and recent advancements

Hepatic ischemia/reperfusion (I/R) injury occurs in a variety of clinical contexts, including transplantation, liver resection surgery, trauma, and hypovolemic shock. The mechanism of organ damage after I/R has been studied extensively and consists of complex interactions of multiple inflammatory pathways. The major contributors to I/R injury include production of reactive oxygen species, release of proinflammatory cytokines and chemokines, and activation of immune cells to promote inflammation and tissue damage. Recent research has focused on the mechanisms by which these immune responses are initially activated through signaling molecules and their cellular receptors. Thorough understanding of the pathophysiology of liver I/R may yield novel therapeutic strategies to reduce I/R injury and lead to improved clinical outcomes.

No synergistic effect of carbon monoxide and oxygen during static gaseous persufflation preservation of DCD livers

OBJECTIVE

The benefit of carbon monoxide and/or oxygen as applied by controlled, continuous gaseous persufflation during liver preservation on postischemic graft recovery was investigated in an isolated rat liver model.

METHODS

Livers from male Wistar rats were retrieved 30 min after cardiac arrest of the donor and subjected to 18 h of cold storage. Some grafts were subjected to gaseous persufflation during static cold storage either with pure oxygen or with CO dissolved in oxygen. Graft integrity was assessed thereafter upon warm reperfusion in vitro.

RESULTS

Oxygen persufflation significantly reduced cellular enzyme loss and metabolic recovery (bile production and ATP recovery) upon reperfusion by about 50%. The effect was associated with a reduction of vascular perfusion resistance, mitigated gene up-regulation of the mitochondrial stress protein GRP 75, and improved mitochondrial ultra-structure. Similar results were obtained by persufflation with CO in oxygen, while no additive benefit of CO and oxygen could be seen in our model.

CONCLUSION

Hepatocellular injury of cold stored liver grafts can be notably reduced by gaseous ex vivo application of oxygen with or without additional admixture of CO to the isolated organ but no superiority or additive effect is seen with respect to persufflation with oxygen.

Carbon monoxide liberated from CO-releasing molecule (CORM-2) attenuates ischemia/reperfusion (I/R)-induced inflammation in the small intestine

CORM-released CO has been shown to be beneficial in resolution of acute inflammation. The acute phase of intestinal ischemia-reperfusion (I/R) injury is characterized by oxidative stress-related inflammation and leukocyte recruitment. In this study, we assessed the effects and potential mechanisms of CORM-2-released CO in modulation of inflammatory response in the small intestine following I/R-challenge. To this end mice (C57Bl/6) small intestine were challenged with ischemia by occluding superior mesenteric artery (SMA) for 45 min. CORM-2 (8 mg/kg; i.v.) was administered immediately before SMA occlusion. Sham operated mice were injected with vehicle (0.25% DMSO). Inflammatory response in the small intestine (jejunum) was assessed 4 h following reperfusion by measuring tissue levels of TNF-alpha protein (ELISA), adhesion molecules E-selectin and ICAM-1 (Western blot), NF-kappaB activation (EMSA), along with PMN tissue accumulation (MPO assay) and leukocyte rolling/adhesion in the microcirculation of jejunum (intravital microscopy). The obtained results indicate that tissue levels of TNF-alpha, E-selectin and ICAM-1 protein expression, activation of NF-kappaB, and subsequent accumulation of PMN were elevated in I/R-challenged jejunum. The above changes were significantly attenuated in CORM-2-treated mice. Taken together these findings indicate that CORM-2-released CO confers anti-inflammatory effects by interfering with NF-kappaB activation and subsequent up-regulation of vascular pro-adhesive phenotype in I/R-challenged small intestine.

Carbon monoxide-releasing molecule-2 (CORM-2) attenuates acute hepatic ischemia reperfusion injury in rats

Background

Hepatic ischemia-reperfusion injury (I/Ri) is a serious complication occurring during liver surgery that may lead to liver failure. Hepatic I/Ri induces formation of reactive oxygen species, hepatocyte apoptosis, and release of pro-inflammatory cytokines, which together causes liver damage and organ dysfunction. A potential strategy to alleviate hepatic I/Ri is to exploit the potent anti-inflammatory and cytoprotective effects of carbon monoxide (CO) by application of so-called CO-releasing molecules (CORMs). Here, we assessed whether CO released from CORM-2 protects against hepatic I/Ri in a rat model.

Methods

Forty male Wistar rats were randomly assigned into four groups (n = 10). Sham group underwent a sham operation and received saline. I/R group underwent hepatic I/R procedure by partial clamping of portal structures to the left and median lobes with a microvascular clip for 60 minutes, yielding ~70% hepatic ischemia and subsequently received saline. CORM-2 group underwent the same procedure and received 8 mg/kg of CORM-2 at time of reperfusion. iCORM-2 group underwent the same procedure and received iCORM-2 (8 mg/kg), which does not release CO. Therapeutic effects of CORM-2 on hepatic I/Ri was assessed by measuring serum damage markers AST and ALT, liver histology score, TUNEL-scoring of apoptotic cells, NFkB-activity in nuclear liver extracts, serum levels of pro-inflammatory cytokines TNF-α and IL-6, and hepatic neutrophil infiltration.

Results

A single systemic infusion with CORM-2 protected the liver from I/Ri as evidenced by a reduction in serum AST/ALT levels and an improved liver histology score. Treatment with CORM-2 also up-regulated expression of the anti-apoptotic protein Bcl-2, down-regulated caspase-3 activation, and significantly reduced the levels of apoptosis after I/Ri. Furthermore, treatment with CORM-2 significantly inhibited the activity of the pro-inflammatory transcription factor NF-κB as measured in nuclear extracts of liver homogenates. Moreover, CORM-2 treatment resulted in reduced serum levels of pro-inflammatory cytokines TNF-α and IL-6 and down-regulation of the adhesion molecule ICAM-1 in the endothelial cells of liver. In line with these findings, CORM-2 treatment reduced the accumulation of neutrophils in the liver upon I/Ri. Similar treatment with an inactive variant of CORM-2 (iCORM-2) did not have any beneficial effect on the extent of liver I/Ri.

Conclusions

CORM-2 treatment at the time of reperfusion had several distinct beneficial effects on severity of hepatic I/Ri that may be of therapeutic value for the prevention of tissue damage as a result of I/Ri during hepatic surgery.

Gaseous persufflation with carbon monoxide during ischemia protects the isolated liver and enhances energetic recovery

BACKGROUND

The benefit of carbon monoxide as applied by controlled, continuous gaseous persufflation during liver preservation on postischemic graft recovery was investigated in an isolated rat liver model.

METHODS

Livers from male Wistar rats were retrieved 30 min after cardiac arrest of the donor and subjected to 18 h of cold storage. Some grafts were subjected to gaseous persufflation with carbon monoxide (CO, dissolved in nitrogen) during static cold storage at a concentration of 50 ppm or 250 ppm. Graft viability was assessed thereafter upon warm reperfusion in vitro.

RESULTS

CO-persufflation significantly reduced cellular enzyme loss (maximal at 50 ppm) and functional recovery (bile production and energy charge) upon reperfusion by about 50%. The effect was associated with a reduction of free radical-induced lipid peroxidation, lower vascular perfusion resistance, and improved mitochondrial ultrastructure.

CONCLUSION

Viability of cold stored liver grafts can be notably augmented by gaseous ex vivo application of low dose CO to the isolated organ.

Heme oxygenase-1 protects donor livers from ischemia/reperfusion injury: the role of Kupffer cells

AIM

To examine whether heme oxygenase (HO)-1 overexpression would exert direct or indirect effects on Kupffer cells activation, which lead to aggravation of reperfusion injury.

METHODS

Donors were pretreated with cobalt protoporphyrin (CoPP) or zinc protoporphyrin (ZnPP), HO-1 inducer and antagonist, respectively. Livers were stored at 4 degrees C for 24 h before transplantation. Kupffer cells were isolated and cultured for 6 h after liver reperfusion.

RESULTS

Postoperatively, serum transaminases were significantly lower and associated with less liver injury when donors were pretreated with CoPP, as compared with the ZnPP group. Production of the cytokines tumor necrosis factor-alpha and interleukin-6 generated by Kupffer cells decreased in the CoPP group. The CD14 expression levels (RT-PCR/Western blots) of Kupffer cells from CoPP-pretreated liver grafts reduced.

CONCLUSION

The study suggests that the potential utility of HO-1 overexpression in preventing ischemia/reperfusion injury results from inhibition of Kupffer cells activation.

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.

Protective effects of a carbon monoxide-releasing molecule (CORM-3) during hepatic cold preservation

There is increasing evidence that carbon monoxide (CO), a signaling molecule generated during the degradation of heme by heme oxygenase-1 (HO-1) in biological systems, has a variety of cytoprotective actions, including anti-hypoxic effects at low temperatures. However, during liver cold preservation, a direct effect needs to be established. Here, we designed a study to analyze the role of CO, delivered via a carbon monoxide-releasing molecule (CO-RM) in the maintenance of liver function, and integrity in rats during cold ischemia/reperfusion (CI/R) injury. We used an isolated normothermic perfused liver system (INPL) following a clinically relevant model of ex vivo 48 h cold ischemia stored in a modified University of Wisconsin (UW) solution, to determine the specific effects of CO in a rat model. CO was generated from 50 microM tricarbonylchloro ruthenium-glycinato (CORM-3), a water-soluble transition metal carbonyl that exerts pharmacological activities via the liberation of controlled amounts of CO in biological systems. The physiological effects of CORM-3 were confirmed by the parallel use of a specific inactive compound (iCORM-3), which does not liberate CO in the cellular environment. CORM-3 addition was found to prevent the injury caused by cold storage by improving significantly the perfusion flow during reperfusion (by almost 90%), and by decreasing the intrahepatic resistance (by 88%) when compared with livers cold preserved in UW alone. Also, CORM-3 supplementation preserved good metabolic capacity as indicated by hepatic oxygen consumption, glycogen content, and release of lactate dehydrogenase. Liver histology was also partially preserved by CORM-3 treatment.

CONCLUSIONS

These findings suggest that CO-RM could be utilized as adjuvant therapeutics in UW solutions to limit the injury sustained by donor livers during cold storage prior to transplantation, as has been similarly proposed for the heart, and kidney.

Heme oxygenase-1/carbon monoxide: from metabolism to molecular therapy

Heme oxygenase-1 (HO-1), a ubiquitous inducible stress-response protein, serves a major metabolic function in heme turnover. HO activity cleaves heme to form biliverdin-IXalpha, carbon monoxide (CO), and iron. Genetic experiments have revealed a central role for HO-1 in tissue homeostasis, protection against oxidative stress, and in the pathogenesis of disease. Four decades of research have witnessed not only progress in elucidating the molecular mechanisms underlying the regulation and function of this illustrious enzyme, but also have opened remarkable translational applications for HO-1 and its reaction products. CO, once regarded as a metabolic waste, can act as an endogenous mediator of cellular signaling and vascular function. Exogenous application of CO by inhalation or pharmacologic delivery can confer cytoprotection in preclinical models of lung/vascular injury and disease, based on anti-apoptotic, anti-inflammatory, and anti-proliferative properties. The bile pigments, biliverdin and bilirubin, end products of heme degradation, have also shown potential as therapeutics in vascular disease based on anti-inflammatory and anti-proliferative activities. Further translational and clinical trials research will unveil whether the HO-1 system or any of its reaction products can be successfully applied as molecular medicine in human disease.

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.

Inhalation of carbon monoxide ameliorates collagen-induced arthritis in mice and regulates the articular expression of IL-1beta and MCP-1

Carbon monoxide (CO), long considered a toxic gas, has recently been shown to mediate anti-inflammatory effects in various animal models. The aim of this study was to investigate whether the inhalation of CO ameliorated collagen-induced arthritis (CIA) in mice. CIA was induced in female DBA/1 mice by the injection of an anti-type II collagen antibody and lipopolysaccharide. The CO treatment group was exposed to CO gas at a concentration of 200 ppm in a closed cage starting on the day of the injection with an anti-type II collagen antibody and throughout the remaining study period. The clinical arthritis scores was examined daily for swelling of the paws as a sign of arthritis. For histopathology, the sections of the hind legs were evaluated by hematoxylin-eosin staining. Moreover, we evaluated the expression of interleukin (IL)-1beta and monocyte chemoattractant protein-1 (MCP-1) mRNA in the hind paws. Both clinical arthritis scores as well as histological findings of joint inflammation were significantly reduced in mice treated with CO gas inhalation compared to untreated mice. Further, CO significantly inhibited the increased expression of IL-1beta and MCP-1 mRNA in paws at day 3 after the induction of arthritis. In conclusion, the inhalation of CO protected mice from the synovial inflammation of CIA. Based on these data, the beneficial effects of CO in murine RA model may be attributed to its anti-inflammatory properties.