Administration of a CO-releasing molecule induces late preconditioning against myocardial infarction

Metal-based carbon monoxide releasing molecules with promising cytotoxic properties

Carbon monoxide, the "silent killer" gas, is increasingly recognised as an important signalling molecule in human physiology, which has beneficial biological properties. A particular way of achieving controlled CO administration is based on the use of biocompatible molecules that only release CO when triggered by internal or external factors. These approaches include the development of pharmacologically effective prodrugs known as CO releasing molecules (CORMs), which can supply biological systems with CO in well-regulated doses. An overview of transition metal-based CORMs with cytotoxic properties is here reported. The mechanisms at the basis of the biological activities of these molecules and their potential therapeutical applications with respect to their stability and CO releasing properties have been discussed. The activation of metal-based CORMs is determined by the type of metal and by the nature and features of the auxiliary ligands, which affect the metal core electronic density and therefore the prodrug resistance towards oxidation and CO release ability. A major role in regulating the cytotoxic properties of these CORMs is played by CO and/or CO-depleted species. However, several mysteries concerning the cytotoxicity of CORMs remain as intriguing questions for scientists.

Clinical Applications for Gasotransmitters in the Cardiovascular System: Are We There Yet?

Ischemia is the underlying mechanism in a wide variety of acute and persistent pathologies. As such, understanding the fine intracellular events occurring during (and after) the restriction of blood supply is pivotal to improving the outcomes in clinical settings. Among others, gaseous signaling molecules constitutively produced by mammalian cells (gasotransmitters) have been shown to be of potential interest for clinical treatment of ischemia/reperfusion injury. Nitric oxide (NO and its sibling, HNO), hydrogen sulfide (H2S), and carbon monoxide (CO) have long been proven to be cytoprotective in basic science experiments, and they are now awaiting confirmation with clinical trials. The aim of this work is to review the literature and the clinical trials database to address the state of development of potential therapeutic applications for NO, H2S, and CO and the clinical scenarios where they are more promising.

Mitochondria-Targeted Nanosystem with Reactive Oxygen Species-Controlled Release of CO to Enhance Photodynamic Therapy of PCN-224 by Sensitizing Ferroptosis

The apoptosis-resistant mechanism of photodynamic therapy (PDT) usually results in limited therapeutic efficacy. The development of new strategies for sensitizing targeted ferroptosis that bypass apoptosis resistance is of great significance to improve the antitumor efficacy of PDT. In this study, a novel amphiphilic copolymer whose main chain contains reactive oxygen species (ROS)-responsive groups and the end of side chains contains triphenylphosphine is synthesized, to encapsulate porphyrinic metal-organic framework PCN-224 via self-assembly which are hydrothermally synthesized by coordination of zirconium (IV) with tetra-kis(4-caboxyphenyl) porphyrin, and loaded carbon monoxide releasing molecule 401 (CORM-401) by their hollow structures (PCN-CORM), and finally, surface-coated with hyaluronic acid. The nanosystem can sequentially localize to mitochondria which is an important target to induce apoptosis and ferroptosis in cancer cells. Upon excitation with near-infrared light, PCN-224 is activated to produce amounts of ROS, and simultaneously triggers the rapid intracellular release of CO. More importantly, the released CO can sensitize ferroptosis and promote apoptosis to significantly enhance the antitumor efficacy of PCN-224 both in vitro and in vivo. These results illustrate that the mitochondria-targeted drug delivery system combined PDT with CO leads to an effective antitumor efficacy, which maybe a promising way to enhance the treatment efficiency of PDT.

Association between ambient carbon monoxide levels and hospitalization costs of patients with myocardial infarction: Potential effect modification by ABO blood group

Previous researches have reported the association between air pollution and various diseases. However, few researches have investigated whether air pollutants are associated with the economic loss resulting from patients' hospitalization, especially the economic loss of hospitalization due to acute cardiovascular events. The purpose of our research was to explore the association between the levels of carbon monoxide (CO), taken as an index of pollution, and the hospitalization costs of myocardial infarction (MI), and the potential effect modification by the ABO blood group. A total of 3237 MI inpatients were included in this study. A multiple linear regression model was used to evaluate the association between ambient CO levels and hospitalization costs of MI patients. Moreover, we performed stratified analyses by age, gender, body mass index (BMI), season, hypertension, and ABO blood types. There was a positive association between the levels of CO in the air and the costs of hospitalization caused by MI. Furthermore, such association was stronger in males, BMI ≥25, <65 years, with hypertension, and non-O blood group. Interestingly, we found the association was particularly significant in patients with blood group B. Overall, our study first found that ambient CO levels could have an impact on the hospitalization costs for MI patients, and those with blood group B can be more sensitive.

Homocysteine, Vitamins B6 and Folic Acid in Experimental Models of Myocardial Infarction and Heart Failure—How Strong Is That Link?

Cardiovascular diseases are the leading cause of death and the main cause of disability. In the last decade, homocysteine has been found to be a risk factor or a marker for cardiovascular diseases, including myocardial infarction (MI) and heart failure (HF). There are indications that vitamin B6 plays a significant role in the process of transsulfuration in homocysteine metabolism, specifically, in a part of the reaction in which homocysteine transfers a sulfhydryl group to serine to form α-ketobutyrate and cysteine. Therefore, an elevated homocysteine concentration (hyperhomocysteinemia) could be a consequence of vitamin B6 and/or folate deficiency. Hyperhomocysteinemia in turn could damage the endothelium and the blood vessel wall and induce worsening of atherosclerotic process, having a negative impact on the mechanisms underlying MI and HF, such as oxidative stress, inflammation, and altered function of gasotransmitters. Given the importance of the vitamin B6 in homocysteine metabolism, in this paper, we review its role in reducing oxidative stress and inflammation, influencing the functions of gasotransmitters, and improving vasodilatation and coronary flow in animal models of MI and HF.

Carbon monoxide releasing molecule-2 suppresses stretch-activated atrial natriuretic peptide secretion by activating large-conductance calcium-activated potassium channels

Carbon monoxide (CO) is a known gaseous bioactive substance found across a wide array of body systems. The administration of low concentrations of CO has been found to exert an anti-inflammatory, anti-apoptotic, anti-hypertensive, and vaso-dilatory effect. To date, however, it has remained unknown whether CO influences atrial natriuretic peptide (ANP) secretion. This study explores the effect of CO on ANP secretion and its associated signaling pathway using isolated beating rat atria. Atrial perfusate was collected for 10 min for use as a control, after which high atrial stretch was induced by increasing the height of the outflow catheter. Carbon monoxide releasing molecule-2 (CORM-2; 10, 50, 100 µM) and hemin (HO-1 inducer; 0.1, 1, 50 µM), but not CORM-3 (10, 50, 100 µM), decreased high stretch-induced ANP secretion. However, zinc porphyrin (HO-1 inhibitor) did not affect ANP secretion. The order of potency for the suppression of ANP secretion was found to be hemin > CORM-2 >> CORM-3. The suppression of ANP secretion by CORM-2 was attenuated by pretreatment with 5-hydroxydecanoic acid, paxilline, and 1H-[1,2,4] oxadiazolo [4,3-a] quinoxalin-1-one, but not by diltiazem, wortmannin, LY-294002, or NG-nitro-L-arginine methyl ester. Hypoxic conditions attenuated the suppressive effect of CORM-2 on ANP secretion. In sum, these results suggest that CORM-2 suppresses ANP secretion via mitochondrial K_ATP channels and large conductance Ca²⁺-activated K⁺ channels.

In vivo therapeutic genome editing via CRISPR/Cas9 magnetoplexes for myocardial infarction

CRISPR/Cas9-mediated gene-editing technology has gained attention as a new therapeutic method for intractable diseases. However, the use of CRISPR/Cas9 for cardiac conditions such as myocardial infarction remains challenging due to technical and biological barriers, particularly difficulties in delivering the system and targeting genes in the heart. In the present study, we demonstrated the in vivo efficacy of the CRISPR/Cas9 magnetoplexes system for therapeutic genome editing in myocardial infarction. First, we developed CRISPR/Cas9 magnetoplexes that magnetically guided CRISPR/Cas9 system to the heart for efficient in vivo therapeutic gene targeting during heart failures. We then demonstrated that the in vivo gene targeting of miR34a via these CRISPR/Cas9 magnetoplexes in a mouse model of myocardial infarction significantly improved cardiac repair and regeneration to facilitate improvements in cardiac function. These results indicated that CRISPR/Cas9 magnetoplexes represent an effective in vivo therapeutic gene-targeting platform in the myocardial infarction of heart, and that this strategy may be applicable for the treatment of a broad range of cardiac failures.

Carbon monoxide and a change of heart

The relationship between carbon monoxide and the heart has been extensively studied in both clinical and preclinical settings. The Food and Drug Administration (FDA) is keenly focused on the ill effects of carbon monoxide on the heart when presented with proposals for clinical trials to evaluate efficacy of this gasotransmitter in a various disease settings. This review provides an overview of the rationale that examines the actions of the FDA when considering clinical testing of CO, and contrast that with the continued accumulation of data that clearly show not only that CO can be used safely, but is potently cardioprotective in clinically relevant small and large animal models. Data emerging from Phase I and Phase II clinical trials argues against CO being dangerous to the heart and thus it needs to be redefined and evaluated as any other substance being proposed for use in humans. More than twenty years ago, the belief that CO could be used as a salutary molecule was ridiculed by experts in physiology and medicine. Like all agents designed for use in humans, careful pharmacology and safety are paramount, but continuing to hinder progress based on long-standing dogma in the absence of data is improper. Now, CO is being tested in multiple clinical trials using innovative delivery methods and has proven to be safe. The hope, based on compelling preclinical data, is that it will continue to be evaluated and ultimately approved as an effective therapeutic.

Isoflurane and low-level carbon monoxide exposures increase expression of pro-survival miRNA in neonatal mouse heart

Anesthetics such as isoflurane are known to cause apoptosis in the developing mammalian brain. However, isoflurane may have protective effects on the heart via relieving ischemia and downregulating genes related to apoptosis. Ischemic preconditioning, e.g. through the use of low levels of carbon monoxide (CO), has promise in preventing ischemia-reperfusion injury and cell death. However, it is still unclear how it either triggers the stress response in neonatal hearts. For this reason, thirty-three microRNAs (miRNAs) known to be differentially expressed following anesthesia and/or ischemic or hypoxic heart damage were investigated in the hearts from neonatal mice exposed to isoflurane or low level of CO, using an air-exposed control group. Only miR-93-5p increased with isoflurane exposure, which may be associated with the suppression of cell death, autophagy, and inflammation. By contrast, twelve miRNAs were differentially expressed in the heart following CO treatment. Many miRNAs previously shown to be responsible for suppressing cell death, autophagy, and myocardial hypertrophy were upregulated (e.g., 125b-3p, 19-3p, and 21a-5p). Finally, some miRNAs (miR-103-3p, miR-1a-3p, miR-199a-1-5p) which have been implicated in regulating energy balance and cardiac contraction were also differentially expressed. Overall, this study demonstrated that CO-mediated miRNA regulation may promote ischemic preconditioning and cardioprotection based on the putative protective roles of the differentially expressed miRNAs explored herein and the consistency of these results with those that have shown positive effects of CO on heart viability following anesthesia and ischemia-reperfusion stress.

Targeting Heme Oxygenase-1 in Cardiovascular and Kidney Disease

Heme oxygenase (HO) plays an important role in the cardiovascular system. It is involved in many physiological and pathophysiological processes in all organs of the cardiovascular system. From the regulation of blood pressure and blood flow to the adaptive response to end-organ injury, HO plays a critical role in the ability of the cardiovascular system to respond and adapt to changes in homeostasis. There have been great advances in our understanding of the role of HO in the regulation of blood pressure and target organ injury in the last decade. Results from these studies demonstrate that targeting of the HO system could provide novel therapeutic opportunities for the treatment of several cardiovascular and renal diseases. The goal of this review is to highlight the important role of HO in the regulation of cardiovascular and renal function and protection from disease and to highlight areas in which targeting of the HO system needs to be translated to help benefit patient populations.

Programmed ROS/CO-releasing nanomedicine for synergetic chemodynamic-gas therapy of cancer

BACKGROUND

To improve the outcome of cancer treatment, the combination of multiple therapy models has proved to be effective and promising. Gas therapy (GT) and chemodynamic therapy (CDT), mainly targeting the mitochondrion and nucleus, respectively, are two emerging strategy for anti-cancer. The development of novel nanomedicine for integrating these new therapy models is greatly significant and highly desired.

METHODS

A new nanomedicine is programmed by successive encapsulation of MnO₂ nanoparticles and iron carbonyl (FeCO) into mesoporous silica nanoparticle. By decoding the nanomedicine, acidity in the lysosome drives MnO₂ to generate ROS, ·OH among which further triggers the decomposition of FeCO into CO, realizing the effective combination of chemodynamic therapy with gas therapy for the first time.

RESULTS

Acidity in the TEM drives MnO₂ to generate ROS, ∙OH among which further triggers the decomposition of FeCO into CO, realizing the effective combination of CDT and CDGT. The co-released ROS and CO do damage to DNA and mitochondria of various cancer cells, respectively. The mitochondrial damage can effectively cut off the ATP source required for DNA repair, causing a synergetic anti-cancer effect in vitro and in vivo.

CONCLUSIONS

The combination of CDT and CDGT causing a synergetic anti-cancer effect in vitro and in vivo. The proposed therapy concept and nanomedicine designing strategy might open a new window for engineering high-performance anti-cancer nanomedicine.

A series of Mn(i) photo-activated carbon monoxide-releasing molecules with benzimidazole coligands: synthesis, structural characterization, CO releasing properties and biological activity evaluation

Five Mn(i) photo-activated carbon monoxide-releasing molecules were synthesized by reactions of MnBr(CO)₅ with L1–L4, and characterized via single crystal X-ray diffraction, ¹H-NMR, ¹³C-NMR, IR, UV-vis and fluorescence spectroscopy.

Modulation of the monocyte/macrophage system in heart failure by targeting heme oxygenase-1

Upon myocardial infarction (MI) immune system becomes activated by extensive necrosis of cardiomyocytes releasing intracellular molecules called damage-associated molecular patterns. Overactive and prolonged immune responses are likely to be responsible for heart failure development and progression in patients surviving the ischemic episode. Heme oxygenase-1 (HO-1) plays a crucial role in heme degradation and in this way releases carbon monoxide, free iron, and biliverdin. This stress-inducible enzyme is induced by various oxidative and inflammatory signals. Consequently, biological actions of HO-1 are not limited to degradation of a toxic heme released from hemoproteins, but also provide an adaptive cellular response against chronic inflammation and oxidative injury. Indeed, the immunomodulatory and anti-inflammatory properties of HO-1 were demonstrated in several experimental studies, as well as in human cases of genetic HO-1 deficiency. HO-1 was shown to suppress the production, myocardial infiltration and inflammatory properties of monocytes and macrophages what resulted in limitation of post-MI cardiac damage. This review specifically addresses the role of HO-1, heme and its degradation products in macrophage biology and post-ischemic cardiac repair. A more complete understanding of these mechanisms is essential to develop new therapeutic approaches.

Intelligent Metal Carbonyl Metal-Organic Framework Nanocomplex for Fluorescent Traceable H2 O2 -Triggered CO Delivery

The recognized therapeutic benefits from carbon monoxide (CO) have caused booming attention to develop a CO therapy for various major diseases, such as cancer. However, the controlled release of CO gas and the monitoring of the CO release are vitally important to the on-demand CO administration for a safe and efficient therapy, but greatly challenging. In this work, a new CO-releasing nanocomplex was constructed by the adsorption and coordination of manganese carbonyl ([MnBr(CO)₅ ], abbreviated as MnCO) with a Ti-based metal-organic framework (Ti-MOF) to realize an intratumoral H₂ O₂ -triggered CO release and real-time CO release monitoring by fluorescence imaging. A high CO prodrug loading capacity (0.532 g MnCO per gram Ti-MOF) is achieved due to the high surface area of Ti-MOF, and the intracellular H₂ O₂ -triggered CO release from the MnCO@Ti-MOF is realized to enable the nanocomplex selectively release CO in tumor cells and kill tumor cells rather than normal cells. Particularly significant is that the real-time fluorescence imaging monitoring of the CO release is realized based on an annihilation effect of the fluorescence after MnCO loading into Ti-MOF and an activation effect of the fluorescence after CO release from Ti-MOF. The quantitative relationship between the fluorescence intensity and the released CO amount is established in great favor of guiding on-demand CO administration. The results demonstrate the advantage of versatile MOFs for high efficient CO delivery and monitoring, which is critical for the improvement of the effectiveness of future therapeutic application.

Cellular and molecular approaches to enhance myocardial recovery after myocardial infarction

Reperfusion therapy has resulted in significant improvement in post-myocardial infarction morbidity and mortality in over the last 4 decades. Nonetheless, it is well recognized that simply restoring patency of the epicardial artery may not stop or reverse damage at microvascular level, and myocardial salvage is often suboptimal. Numerous efforts have been undertaken to elucidate the mechanisms underlying extensive myonecrosis to facilitate the discovery of therapies to provide additional and incremental benefits over current therapeutic pathways. To date, conclusively effective strategies to promote myocardial recovery have not yet been established. Novel approaches are investigating the foundational cellular and molecular bases of myocardial ischemia and irreversible injury. Herein, we review the emerging concepts and proposed therapies that may improve myocardial protection and reduce infarct size. We examine the preclinical and clinical evidence for reduced infarct size with these strategies, including anti-inflammatory agents, intracellular ion channel modulators, agents affecting the reperfusion injury salvage kinase (RISK) and nitric oxide signaling pathways, modulators of mitochondrial function, anti-apoptotic agents, and stem cell and gene therapy. We review the potential reasons of failures to date and the potential for new strategies to further promote myocardial recovery and improve prognosis.

NO, CO and H2 S: What about gasotransmitters in fish and amphibian heart?

The gasotransmitters nitric oxide (NO), carbon monoxide (CO), and hydrogen sulphide (H₂ S), long considered only toxicant, are produced in vivo during the catabolism of common biological molecules and are crucial for a large variety of physiological processes. Mounting evidence is emerging that in poikilotherm vertebrates, as in mammals, they modulate the basal performance of the heart and the response to stress challenges. In this review, we will focus on teleost fish and amphibians to highlight the evolutionary importance in vertebrates of the cardiac control elicited by NO, CO and H₂ S, and the conservation of the intracellular cascades they activate. Although many gaps are still present due to discontinuous information, we will use examples obtained by studies from our and other laboratories to illustrate the complexity of the mechanisms that, by involving gasotransmitters, allow beat-to-beat, short-, medium- and long-term cardiac homoeostasis. By presenting the latest data, we will also provide a framework in which the peculiar morpho-functional arrangement of the teleost and amphibian heart can be considered as a reference tool to decipher cardiac regulatory networks which are difficult to explore using more conventional vertebrates, such as mammals.

Cardiovascular effects of gasotransmitter donors

Gasotransmitters represent a subfamily of the endogenous gaseous signaling molecules that include nitric oxide (NO), carbon monoxide (CO), and hydrogen sulphide (H(2)S). These particular gases share many common features in their production and function, but they fulfill their physiological tasks in unique ways that differ from those of classical signaling molecules found in tissues and organs. These gasotransmitters may antagonize or potentiate each other's cellular effects at the level of their production, their downstream molecular targets and their direct interactions. All three gasotransmitters induce vasodilatation, inhibit apoptosis directly or by increasing the expression of anti-apoptotic genes, and activate antioxidants while inhibiting inflammatory actions. NO and CO may concomitantly participate in vasorelaxation, anti-inflammation and angiogenesis. NO and H(2)S collaborate in the regulation of vascular tone. Finally, H(2)S may upregulate the heme oxygenase/carbon monoxide (HO/CO) pathway during hypoxic conditions. All three gasotransmitters are produced by specific enzymes in different cell types that include cardiomyocytes, endothelial cells and smooth muscle cells. As translational research on gasotransmitters has exploded over the past years, drugs that alter the production/levels of the gasotransmitters themselves or modulate their signaling pathways are now being developed. This review is focused on the cardiovascular effects of NO, CO, and H(2)S. Moreover, their donors as drug targeting the cardiovascular system are briefly described.

Heme Oxygenases in Cardiovascular Health and Disease

Heme oxygenases are composed of two isozymes, Hmox1 and Hmox2, that catalyze the degradation of heme to carbon monoxide (CO), ferrous iron, and biliverdin, the latter of which is subsequently converted to bilirubin. While initially considered to be waste products, CO and biliverdin/bilirubin have been shown over the last 20 years to modulate key cellular processes, such as inflammation, cell proliferation, and apoptosis, as well as antioxidant defense. This shift in paradigm has led to the importance of heme oxygenases and their products in cell physiology now being well accepted. The identification of the two human cases thus far of heme oxygenase deficiency and the generation of mice deficient in Hmox1 or Hmox2 have reiterated a role for these enzymes in both normal cell function and disease pathogenesis, especially in the context of cardiovascular disease. This review covers the current knowledge on the function of both Hmox1 and Hmox2 at both a cellular and tissue level in the cardiovascular system. Initially, the roles of heme oxygenases in vascular health and the regulation of processes central to vascular diseases are outlined, followed by an evaluation of the role(s) of Hmox1 and Hmox2 in various diseases such as atherosclerosis, intimal hyperplasia, myocardial infarction, and angiogenesis. Finally, the therapeutic potential of heme oxygenases and their products are examined in a cardiovascular disease context, with a focus on how the knowledge we have gained on these enzymes may be capitalized in future clinical studies.

Ruthenium-based nitric oxide-donating and carbon monoxide-donating molecules

Objectives

Over the past few years, the use of metallocomplexes for medical purposes has considerably grown. Because of its favourable characteristics, ruthenium has taken a significant place in this expanding field of research. Several ruthenium-containing metal compounds have been developed as delivery agents of physiological important molecules such as nitric oxide (NO) and carbon monoxide (CO).

Key findings

This review focuses on the (vaso)relaxant capacity of ruthenium-based NO-donating and CO-donating molecules in view of their potential usefulness in the treatment of cardiovascular diseases and erectile dysfunction.

Summary

Ruthenium seems to be a valuable candidate for the design of NO-donating and CO-donating molecules. To date, ruthenium remains of interest in drug research as the search for new alternatives is still necessary.

ENDOGENOUS CARBON MONOXIDE CONCENTRATION IN BLOOD ELEVATES IN ACUTE CORONARY SYNDROME OF NONSMOKER POPULATION

BACKGROUND

Carbon monoxide (CO) was previously only considered as a highly toxic pollutant since it binds to hemoglobin with high affinity. Recently, however, it has been recognized as a signaling molecule with regulatory roles in many physiological and pathophysiological processes within the cardiovascular system. The aim of this study was to clarify the behavior of CO in patients with acute coronary syndrome (ACS).

METHODS

We assessed 235 patients with suspected ACS, 98 smokers (88 male, 62 ± 14 years) and 137 nonsmokers (77 male, 72 ± 13 years), who had undergone emergent cardiac catheterization and blood sampling for calculation of carboxyhemoglobin (COHb). Patients were categorized into 4 groups: smoking patients with ACS (n=77), smoking patients without ACS (n=21), non-smoking patients with ACS (n=97), and non-smoker patients without ACS (n=40). We investigated whether biomarkers were related to COHb levels.

RESULTS

LogCOHb was significantly higher in the smoking patients compared to non-smoking patients (0.30 ± 0.12 vs. 0.45 ± 0.18, P < 0.01). Interestingly, among the non-smoking patients, COHb was increased in the ACS patients compared to the non ACS patients (0.31 ± 0.12 vs. 0.25 ± 0.12 P < 0.01). In contrast, among the smoking patients, there was no difference in COHb between the ACS and non-ACS patients (0.45 ± 0.18 vs. 0.44 ± 0.18, n.s.). There were no correlations between COHb and any of the biomarkers.

CONCLUSIONS

These results suggest that endogenous CO may be useful to assess the risk of cardiovascular stress.

Synthesis and Characterization of a "Turn-On" photoCORM for Trackable CO Delivery to Biological Targets

A designed photoactive CO releasing molecule (photoCORM), namely, fac-[MnBr(CO)3(pbt)] (1, pbt = 2-(2-pyridyl)benzothiazole), promotes CO-induced death of MDA-MB-231 human breast cancer cells upon illumination with broadband visible light. The CO release from this photoCORM can be tracked by rise in fluorescence within the cellular matrix due to deligation of the pbt ligand. The results of this study suggest the potential of 1 in eradication of cancer cells through CO delivery.

Exogenous carbon monoxide suppresses Escherichia coli vitality and improves survival in an Escherichia coli-induced murine sepsis model

AIM

Endogenous carbon monoxide (CO) has been shown to modulate inflammation and inhibit cytokine production both in vivo and in vitro. The aim of this study was to examine whether exogenous carbon monoxide could suppress the vitality of Escherichia coli (E coli) and improve the survival rate in an E coli-induced murine sepsis model.

METHODS

ICR mice were infected with E coli, and immediately injected intravenously with carbon monoxide releasing molecule-2 (CORM-2, 8 mg/kg) or inactive CORM-2 (8 mg/kg). The survival rate was monitored 6 times daily for up to 36 h. The blood samples, liver and lung tissues were collected at 6 h after the infection. Bacteria in peritoneal lavage fluid, blood and tissues were enumerated following culture. Tissue iNOS mRNA expression was detected using RT-PCR. NF-κB expression was detected with Western blotting.

RESULTS

Addition of CORM-2 (200 and 400 μmol/L) into culture medium concentration-dependently suppressed the growth of E coli and decreased the colony numbers, but inactive CORM-2 had no effect. Treatment of the infected mice with CORM-2 significantly increased the survival rate to 55%, while all the infected mice treated with inactive CORM-2 died within 36 h. E coli infection caused severe pathological changes in liver and lungs, and significantly increased serum transaminases, lipopolysaccharide, TNF-α and IL-1β levels, as well as myeloperoxidase activity, TNF-α and IL-1β levels in the major organs. Meanwhile, E coli infection significantly increased the number of colonies and the expression of iNOS mRNA and NF-κB in the major organs. All these abnormalities were significantly attenuated by CORM-2 treatment, while inactive CORM-2 was ineffective.

CONCLUSION

In addition directly suppressing E coli, CORM-2 protects the liver and lungs against E coli-induced sepsis in mice, thus improving their survival.

Heme oxygenase-1: an emerging therapeutic target to curb cardiac pathology

Activation of heme oxygenase-1 (HO-1), a heme-degrading enzyme responsive to a wide range of cellular stress, is traditionally considered to convey adaptive responses to oxidative stress, inflammation and vasoconstriction. These diversified effects are achieved through the degradation of heme to carbon monoxide (CO), biliverdin (which is rapidly converted to bilirubin by biliverdin reductase) and ferric iron. Recent findings have added antiproliferative and angiogenic effects to the list of HO-1/CO actions. HO-1 along with its reaction products bilirubin and CO are protective against ischemia-induced injury (myocardial infarction, ischemia-reperfusion (IR)-injury and post-infarct structural remodelling). Moreover, HO-1, and CO in particular, possess acute antihypertensive effects. As opposed to these curative potentials, the long-believed protective effect of HO-1 in cardiac remodelling in response to pressure overload and type 2 diabetes mellitus (DM) has been questioned by recent work. These challenges, coupled with emerging regulatory mechanisms, motivate further in-depth studies to help understand untapped layers of HO-1 regulation and action. The outcomes of these efforts may shed new light on critical mechanisms that could be used to harness the protective potential of this enzyme for the therapeutic benefit of patients suffering from such highly prevalent cardiovascular disorders.

The role of gasotransmitters NO, H2S and CO in myocardial ischaemia/reperfusion injury and cardioprotection by preconditioning, postconditioning and remote conditioning

Ischaemic heart disease is one of the leading causes of morbidity and mortality worldwide. The development of cardioprotective therapeutic agents remains a partly unmet need and a challenge for both medicine and industry, with significant financial and social implications. Protection of the myocardium can be achieved by mechanical vascular occlusions such as preconditioning (PC), when brief episodes of ischaemia/reperfusion (I/R) are experienced prior to ischaemia; postconditioning (PostC), when the brief episodes are experienced at the immediate onset of reperfusion; and remote conditioning (RC), when the brief episodes are experienced in another vascular territory. The elucidation of the signalling pathways, which underlie the protective effects of PC, PostC and RC, would be expected to reveal novel molecular targets for cardioprotection that could be modulated by pharmacological agents to prevent reperfusion injury. Gasotransmitters including NO, hydrogen sulphide (H2S) and carbon monoxide (CO) are a growing family of regulatory molecules that affect physiological and pathological functions. NO, H2S and CO share several common properties; they are beneficial at low concentrations but hazardous in higher amounts; they relax smooth muscle cells, inhibit apoptosis and exert anti-inflammatory effects. In the cardiovascular system, NO, H2S and CO induce vasorelaxation and promote cardioprotection. In this review article, we summarize current knowledge on the role of the gasotransmitters NO, H2S and CO in myocardial I/R injury and cardioprotection provided by conditioning strategies and highlight future perspectives in cardioprotection by NO, H2S, CO, as well as their donor molecules.

The multifunctional role and therapeutic potential of HO-1 in the vascular endothelium

SIGNIFICANCE

Heme oxygenases (HO-1 and HO-2) catalyze the degradation of the pro-oxidant heme into carbon monoxide (CO), iron, and biliverdin, which is subsequently converted to bilirubin. In the vasculature, particular interest has focused on antioxidant and anti-inflammatory properties of the inducible HO-1 isoform in the vascular endothelium. This review will present evidence that illustrates the potential therapeutic significance of HO-1 and its products, with special emphasis placed on their beneficial effects on the endothelium in vascular diseases.

RECENT ADVANCES

The understanding of the molecular basis for the regulation and functions of HO-1 has led to the identification of a variety of drugs that increase HO-1 activity in the vascular endothelium. Moreover, therapeutic delivery of HO-1 products CO, biliverdin, and bilirubin has been shown to have favorable effects, notably on endothelial cells and in animal models of vascular disease.

CRITICAL ISSUES

To date, mechanistic data identifying the downstream target genes utilized by HO-1 and its products to exert their actions remain relatively sparse. Likewise, studies in man to investigate the efficacy of therapeutics known to induce HO-1 or the consequences of the tissue-specific delivery of CO or biliverdin/bilirubin are rarely performed.

FUTURE DIRECTIONS

Based on the promising in vivo data from animal models, clinical trials to explore the safety and efficacy of the therapeutic induction of HO-1 and the delivery of its products should now be pursued further, targeting, for example, patients with severe atherosclerotic disease, ischemic limbs, restenosis injury, or at high risk of organ rejection.

Regulatory effect and mechanisms of carbon monoxide-releasing molecule II on hepatic energy metabolism in septic mice

AIM: To investigate the possible mechanisms of exogenous carbon monoxide-releasing molecule II (CORM-2) intervention on hepatic energy metabolism in experimental sepsis.

METHODS: Forty-eight C57BL/6 mice were randomly divided into four groups (n = 12): sham group; cecal ligation and puncture (CLP) group; CLP + CORM-2 group and CLP + iCORM-2 (inactive CORM-2) group. Survival rates were determined after 72 h. Twenty-four similarly treated mice (n = 6 in each group) were assayed for post-operative continuous blood glucose in the first 36 h. Thirty-six similarly treated mice (n = 9 in each group) underwent micro-positron emission tomography (PET) scanning after tail vein injection of ¹⁸F-fluorodeoxyglucose (FDG) 24 h after operation. Plasma and liver specimens were collected for assay of liver pathology, alanine transaminase (ALT) and aspartate transaminase (AST) activities. Hepatic glucokinase activity, lactic acid levels and mitochondrial swelling were also determined.

RESULTS: Improved survival was observed in CORM-2 treated mice. Both the CLP and CLP + CORM-2 groups had sustained low blood glucose levels within the first post-operative 36 h. ¹⁸F-FDG micro-PET images showed abnormally high levels of hepatic glucose metabolism (standardized uptake value) in the CLP group (2.76 ± 0.39 vs 0.84 ± 0.14, P < 0.01), which declined to normal levels after CORM-2 intervention (1.29 ± 0.32 vs 2.76 ± 0.39, P < 0.05). glucokinase activity was markedly increased in the CLP group (6.38 ± 0.56 U/g vs 4.60 ± 0.21 U/g, P < 0.01), but was normal after CORM-2 intervention (4.74 ± 0.14 U/g vs 6.38 ± 0.56 U/g, P < 0.05). CORM-2 suppressed plasma lactic acid levels (4.02 ± 0.02 mmol/L vs 7.72 ± 2.37 mmol/L, P < 0.05) and protected hepatic mitochondria in CLP mice. CORM-2 intervention also reduced elevated plasma AST (199.67 ± 11.08 U/L vs 379.67 ± 16.34 U/L, P < 0.05) and ALT (63.67 ± 12.23 U/L vs 112.67 ± 9.74 U/L, P < 0.05) activities in CLP mice.

CONCLUSION: The release of CO molecules by CORM-2 protects mitochondria and maintains a stable level of hepatic glucose metabolism. Thus, CORM-2 improves liver function and survival in septic mice.

Review article: carbon monoxide in gastrointestinal physiology and its potential in therapeutics

BACKGROUND

While carbon monoxide (CO) is a known toxin, it is now recognised that CO is also an important signalling molecule involved in physiology and pathophysiology.

AIMS

To summarise our current understanding of the role of endogenous CO in the regulation of gastrointestinal physiology and pathophysiology, and to potential therapeutic applications of modulating CO.

METHODS

This review is based on a comprehensive search of the Ovid Medline comprehensive database and supplemented by our ongoing studies evaluating the role of CO in gastrointestinal physiology and pathophysiology.

RESULTS

Carbon monoxide derived from haem oxygenase (HO)-2 is predominantly involved in neuromodulation and in setting the smooth muscle membrane potential, while CO derived from HO-1 has anti-inflammatory and antioxidative properties, which protect gastrointestinal smooth muscle from damage caused by injury or inflammation. Exogenous CO is being explored as a therapeutic agent in a variety of gastrointestinal disorders, including diabetic gastroparesis, post-operative ileus, organ transplantation, inflammatory bowel disease and sepsis. However, identifying the appropriate mechanism for safely delivering CO in humans is a major challenge.

CONCLUSIONS

Carbon monoxide is an important regulator of gastrointestinal function and protects the gastrointestinal tract against noxious injury. CO is a promising therapeutic target in conditions associated with gastrointestinal injury and inflammation. Elucidating the mechanisms by which CO works and developing safe CO delivery mechanisms are necessary to refine therapeutic strategies.

MP4CO, a pegylated hemoglobin saturated with carbon monoxide, is a modulator of HO-1, inflammation, and vaso-occlusion in transgenic sickle mice

Transgenic sickle mice expressing β(S) hemoglobin have activated vascular endothelium in multiple organs that exhibits enhanced expression of NF-ĸB and adhesion molecules and promotes microvascular stasis in sickle, but not normal, mice in response to hypoxia/reoxygenation (H/R), or heme. Induction of heme oxygenase-1 (HO-1) or administration of its products, carbon monoxide (CO) or biliverdin, inhibits microvascular stasis in sickle mice. Infusion of human hemoglobin conjugated with polyethylene glycol and saturated with CO (MP4CO) markedly induced hepatic HO-1 activity and inhibited NF-ĸB activation and H/R-induced microvascular stasis in sickle mice. These effects were mediated by CO; saline or MP4 saturated with O2 (MP4OX) had little to no effect on H/R-induced stasis, though unmodified oxyhemoglobin exacerbated stasis. The HO-1 inhibitor, tin protoporphyrin, blocked MP4CO protection, consistent with HO-1 involvement in the protection afforded by MP4CO. MP4CO also induced nuclear factor-erythroid 2 p45-related factor 2 (Nrf2), an important transcriptional regulator of HO-1 and other antioxidant genes. In a heterozygous (hemoglobin-AS) sickle mouse model, intravenous hemin induced cardiovascular collapse and mortality within 120 minutes, which was significantly reduced by MP4CO, but not MP4OX. These data demonstrate that MP4CO induces cytoprotective Nrf2 and HO-1 and decreases NF-ĸB activation, microvascular stasis, and mortality in transgenic sickle mouse models.

Mechanism(s) Involved in Carbon Monoxide-releasing Molecule-2-mediated Cardioprotection During Ischaemia-reperfusion Injury in Isolated Rat Heart

The purpose of the present study was to determine the mechanism(s) involved in carbon monoxide-releasing molecule-2, carbon monoxide-releasing molecule-2-induced cardioprotection. We used the transition metal carbonyl compound carbon monoxide-releasing molecule-2 that can act as carbon monoxide donor in cardiac ischaemia-reperfusion injury model using isolated rat heart preparation. Langendorff's perfused rat hearts when treated with carbon monoxide-releasing molecule-2 (50 μM) for 10 min before global ischaemia exhibited significant reduction in postischaemic levels of myocardial injury markers, creatine kinase and lactate dehydrogenase in coronary effluent. Similarly, pretreatment with carbon monoxide-releasing molecule-2 showed significantly improved postischaemic recovery of heart rate, coronary flow rate, cardiodynamic parameters and reduced infarct size as compared to vehicle control hearts. Perfusion with p38 mitogen-activated protein kinase inhibitor, SB203580, a specific inhibitor of α and β isoform, before and concomitantly with carbon monoxide-releasing molecule-2 treatment abolished carbon monoxide-releasing molecule-2-induced cardioprotection. However, p38 mitogen-activated protein kinase alpha inhibitor, SCIO-469, was unable to inhibit the cardioprotective effect of carbon monoxide-releasing molecule-2. Furthermore, protective effect of carbon monoxide-releasing molecule-2 was significantly inhibited by the protein kinase C inhibitor, chelerythrine, when added before and concomitantly with carbon monoxide-releasing molecule-2. It was also observed that, perfusion with phosphatidylinositol 3-kinase inhibitor, wortmannin, before and concomitantly with carbon monoxide-releasing molecule-2 was not able to inhibit carbon monoxide-releasing molecule-2-induced cardioprotection. Interestingly, we observed that wortmannin perfusion before ischaemia and continued till reperfusion significantly inhibited carbon monoxide-releasing molecule-2-mediated cardioprotection. Our findings suggest that the carbon monoxide-releasing molecule-2 treatment may activate the p38 mitogen-activated protein kinase β and protein kinase C pathways before ischaemia and phosphatidylinositol 3-kinase pathway during reperfusion which may be responsible for the carbon monoxide-releasing molecule-2-mediated cardioprotective effect.

Carbon monoxide stimulates Ca2+ -dependent big-conductance K channels in the cortical collecting duct

We used the patch-clamp technique to examine the role of carbon monoxide (CO) in regulating Ca(2+)-activated big-conductance K (BK) channels in the principal cell of the cortical collecting duct (CCD). Application of CORM3 or CORM2, a CO donor, activated BK channels in the CCD, whereas adding inactivated CORM2/3 had no effect. Superfusion of the CCD with CO-bubbled bath solution also activated the BK channels in the cell-attached patches. The effect of CO on BK channels was not dependent on nitric oxide synthase (NOS) because the effect of CORM3 was also observed in the CCD treated with l-NAME, an agent that inhibits the NOS. Adding a membrane-permeable cGMP analog, 8-bromo-cGMP, significantly increased the BK channel in the CCD. However, inhibition of soluble guanylate cyclase failed to abolish the stimulatory effect of CORM3 on BK channels. Moreover, inhibition of cGMP-dependent protein kinase G did not block the stimulatory effect of CORM3 on the BK channels, suggesting that the stimulatory effect of CO on the BK channels was, at least partially, induced by a cGMP-independent mechanism. Western blot demonstrated that heme oxygenase type 1 (HO-1) and HO-2 were expressed in the kidney. Moreover, a high-K (HK) intake increased the expression of HO-1 but not HO-2 in the kidney. A HK intake also increased renal HO activity defined by NADPH-dependent CO generation following addition of heme in the cell lysate from renal cortex and outer medulla. The role of HO in regulating BK channel activity in the CCD was also suggested by experiments in which application of hemin increased the BK channels. The stimulatory effect of hemin on the BK channels was blocked by SnMP, a HO inhibitor. But, adding CORM3 was still able to activate the BK channels in the presence of SnMP. We conclude that CO activates the BK channels, at least partially, through a NO-cGMP-independent pathway and that HO plays a role in mediating the effect of HK intake on the BK channels in the CCD.

Exogenous carbon monoxide attenuates inflammatory responses in the small intestine of septic mice

AIM: To determine whether the carbon monoxide (CO)-releasing molecules (CORM)-liberated CO suppress inflammatory responses in the small intestine of septic mice.

METHODS: The C57BL/6 mice (male, n = 36; weight 20 ± 2 g) were assigned to four groups in three respective experiments. Sepsis in mice was induced by cecal ligation and puncture (CLP) (24 h). Tricarbonyldichlororuthenium (II) dimer (CORM-2) (8 mg/kg, i.v.) was administrated immediately after induction of CLP. The levels of inflammatory cytokines [interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α)] in tissue homogenates were measured with enzyme-linked immunosorbent assay. The levels of malondialdehyde (MDA) in the tissues were determined. The levels of nitric oxide (NO) in tissue homogenate were measured and the expression levels of intercellular adhesion molecule 1 (ICAM-1) and inducible nitric oxide synthase (iNOS) in the small intestine were also assessed. NO and IL-8 levels in the supernatants were determined after the human adenocarcinoma cell line Caco-2 was stimulated by lipopolysaccharide (LPS) (10 g/mL) for 4 h in vitro.

RESULTS: At 24 h after CLP, histological analysis showed that the ileum and jejunum from CLP mice induced severe edema and sloughing of the villous tips, as well as infiltration of inflammatory cells into the mucosa. Semi-quantitative analysis of histological samples of ileum and jejunum showed that granulocyte infiltration in the septic mice was significantly increased compared to that in the sham group. Administration of CORM-2 significantly decreased granulocyte infiltration. At 24 h after CLP, the tissue MDA levels in the mid-ileum and mid-jejunum significantly increased compared to the sham animals (103.68 ± 23.88 nmol/mL vs 39.66 ± 8.23 nmol/mL, 89.66 ± 9.98 nmol/mL vs 32.32 ± 7.43 nmol/mL, P < 0.01). In vitro administration of CORM-2, tissue MDA levels were significantly decreased (50.65 ± 11.46 nmol/mL, 59.32 ± 6.62 nmol/mL, P < 0.05). Meanwhile, the tissue IL-1β and TNF-α levels in the mid-ileum significantly increased compared to the sham animals (6.66 ± 1.09 pg/mL vs 1.67 ± 0.45 pg/mL, 19.34 ± 3.99 pg/mL vs 3.98 ± 0.87 pg/mL, P < 0.01). In vitro administration of CORM-2, tissue IL-1β and TNF-α levels were significantly decreased (3.87 ± 1.08 pg/mL, 10.45 ± 2.48 pg/mL, P < 0.05). The levels of NO in mid-ileum and mid-jejunum tissue homogenate were also decreased (14.69 ± 2.45 nmol/mL vs 24.36 ± 2.97 nmol/mL, 18.47 ± 2.47 nmol/mL vs 27.33 ± 3.87 nmol/mL, P < 0.05). The expression of iNOS and ICAM-1 in the mid-ileum of septic mice at 24 h after CLP induction significantly increased compared to the sham animals. In vitro administration of CORM-2, expression of iNOS and ICAM-1 were significantly decreased. In parallel, the levels of NO and IL-8 in the supernatants of Caco-2 stimulated by LPS was markedly decreased in CORM-2-treated Caco-2 cells (2.22 ± 0.12 nmol/mL vs 6.25 ± 1.69 nmol/mL, 24.97 ± 3.01 pg/mL vs 49.45 ± 5.11 pg/mL, P < 0.05).

CONCLUSION: CORM-released CO attenuates the inflammatory cytokine production (IL-1β and TNF-α), and suppress the oxidative stress in the small intestine during sepsis by interfering with protein expression of ICAM-1 and iNOS.

Inhaled carbon monoxide provides cerebral cytoprotection in pigs

Carbon monoxide (CO) at low concentrations imparts protective effects in numerous preclinical small animal models of brain injury. Evidence of protection in large animal models of cerebral injury, however, has not been tested. Neurologic deficits following open heart surgery are likely related in part to ischemia reperfusion injury that occurs during cardiopulmonary bypass surgery. Using a model of deep hypothermic circulatory arrest (DHCA) in piglets, we evaluated the effects of CO to reduce cerebral injury. DHCA and cardiopulmonary bypass (CPB) induced significant alterations in metabolic demands, including a decrease in the oxygen/glucose index (OGI), an increase in lactate/glucose index (LGI) and a rise in cerebral blood pressure that ultimately resulted in increased cell death in the neocortex and hippocampus that was completely abrogated in piglets preconditioned with a low, safe dose of CO. Moreover CO-treated animals maintained normal, pre-CPB OGI and LGI and corresponding cerebral sinus pressures with no change in systemic hemodynamics or metabolic intermediates. Collectively, our data demonstrate that inhaled CO may be beneficial in preventing cerebral injury resulting from DHCA and offer important therapeutic options in newborns undergoing DHCA for open heart surgery.

Genetic background, gender, age, body temperature, and arterial blood pH have a major impact on myocardial infarct size in the mouse and need to be carefully measured and/or taken into account: results of a comprehensive analysis of determinants of infarct size in 1,074 mice

In order to determine whether the myocardial response to ischemia/reperfusion (I/R) injury varies depending on genetic background, gender, age, body temperature, and arterial blood pH, we studied 1,074 mice from 19 strains (including 129S6/SvEvTac (129S6), B6/129P2-Ptgs2(tm1Unc), B6/129SvF(2)/J, B6/129/D2, B6/CBAF1, B6/DBA/1JNcr, BALB/c, BPH2/J, C57BL/6/J (B6/J), C3H/DBA, C3H/FB/FF, C3H/HeJ-Pde6b(rd1), FVB/N/J [FVB/N], FVB/B6, FVB/ICR and Crl:ICR/H [ICR]) and distributed them into 69 groups depending on strain and: (1) two phases of ischemic preconditioning (PC); (2) coronary artery occlusion (O) time; (3) gender; (4) age; (5) blood transfusion; (6) core body temperature; and (7) arterial blood pH. Mice underwent O either without (non-preconditioned [naive]) or with prior cyclic O/reperfusion (R) (PC stimulus) consisting of six 4-min O/4-min R cycles 10 min (early PC, EPC) or 24 h (late PC, LPC) prior to 30 or 45-min O and 24 h R. In B6/J and B6/129/D2 mice, almost the entire risk region was infarcted after a 60-min O. Of the naive mouse hearts, B6/ecSOD(WT) and FVB/N mice had infarct sizes significantly smaller than those of the other mice. All strains except FVB/N benefited from the cardioprotection afforded by the early phase of PC; in contrast, development of LPC was inconsistent amongst groups and was strain-dependent. Female gender (1) was associated with reduced infarct size in ICR mice, (2) determined whether LPC developed in ICR mice, and (3) limited the protection afforded by EPC in 129S6 mice. Importantly, mild hypothermia (1 °C decrease in core temperature) and mild acidosis (0.18 decrease in blood pH) resulted in a striking cardioprotective effect in ICR mice: 67.5 and 43.0 % decrease in infarct size, respectively. Replacing blood losses with crystalloid fluids (instead of blood) during surgery also reduced infarct size. To our knowledge, this is the largest analysis of the determinants of infarct size in mice ever published. The results demonstrate that genetic background, gender, age (but not in ICR), body temperature and arterial blood pH have a major impact on infarct size, and thus need to be carefully measured and/or taken into account when designing a study of myocardial infarction in mice; failure to do so makes results uninterpretable. For example, core temperature and blood pH need to be measured, respiratory acidosis (or alkalosis) and hypothermia (or hyperthermia) must be avoided, and comparisons cannot be made between mouse strains or genders that exhibit different susceptibility to I/R injury (e.g., FVB/N male mice and ICR female mice are inherently protected against I/R injury).

The COX-2/PGI2 receptor axis plays an obligatory role in mediating the cardioprotection conferred by the late phase of ischemic preconditioning

Background

Pharmacologic studies with cyclooxygenase-2 (COX-2) inhibitors suggest that the late phase of ischemic preconditioning (PC) is mediated by COX-2. However, nonspecific effects of COX-2 inhibitors cannot be ruled out, and the selectivity of these inhibitors for COX-2 vs. COX-1 is only relative. Furthermore, the specific prostaglandin (PG) receptors responsible for the salubrious actions of COX-2-derived prostanoids remain unclear.

Objective

To determine the role of COX-2 and prostacyclin receptor (IP) in late PC by gene deletion.

Methods

COX-2 knockout (KO) mice (COX-2^−/−), prostacyclin receptor KO (IP^−/−) mice, and respective wildtype (WT, COX-2^+/+ and IP^+/+) mice underwent sham surgery or PC with six 4-min coronary occlusion (O)/4-min R cycles 24 h before a 30-min O/24 h R.

Results

There were no significant differences in infarct size (IS) between non-preconditioned (non-PC) COX-2^+/+, COX-2^−/−, IP^+/+, and IP^−/− mice, indicating that neither COX-2 nor IP modulates IS in the absence of PC. When COX-2^−/− or IP^−/− mice were preconditioned, IS was not reduced, indicating that the protection of late PC was completely abrogated by deletion of either the COX-2 or the IP gene. Administration of the IP selective antagonist, RO3244794 to C57BL6/J (B6) mice 30 min prior to the 30-min O had no effect on IS. When B6 mice were preconditioned 24 h prior to the 30-min O, IS was markedly reduced; however, the protection of late PC was completely abrogated by pretreatment of RO3244794.

Conclusions

This is the first study to demonstrate that targeted disruption of the COX-2 gene completely abrogates the infarct-sparing effect of late PC, and that the IP, downstream of the COX-2/prostanoid pathway, is a key mediator of the late PC. These results provide unequivocal molecular genetic evidence for an essential role of the COX-2/PGI2 receptor axis in the cardioprotection afforded by the late PC.

Carbon monoxide: an unusual drug

The highly toxic gas carbon monoxide (CO) displays many physiological roles in several organs and tissues. Although many diseases, including cancer, hematological diseases, hypertension, heart failure, inflammation, sepsis, neurodegeneration, and sleep disorders, have been linked to abnormal endogenous CO metabolism and functions, CO administration has therapeutic potential in inflammation, sepsis, lung injury, cardiovascular diseases, transplantation, and cancer. Here, insights into the CO-based therapy, characterized by the induction or gene transfer of heme oxygenase-1 and either gas or CO-releasing molecule administration, are reviewed.

Carbon monoxide modulates apoptosis by reinforcing oxidative metabolism in astrocytes: role of Bcl-2

Modulation of cerebral cell metabolism for improving the outcome of hypoxia-ischemia and reperfusion is a strategy yet to be explored. Because carbon monoxide (CO) is known to prevent cerebral cell death; herein the role of CO in the modulation of astrocytic metabolism, in particular, at the level of mitochondria was investigated. Low concentrations of CO partially inhibited oxidative stress-induced apoptosis in astrocytes, by preventing caspase-3 activation, mitochondrial potential depolarization, and plasmatic membrane permeability. CO exposure enhanced intracellular ATP generation, which was accompanied by an increase on specific oxygen consumption, a decrease on lactate production, and a reduction of glucose use, indicating an improvement of oxidative phosphorylation. Accordingly, CO increased cytochrome c oxidase (COX) enzymatic specific activity and stimulated mitochondrial biogenesis. In astrocytes, COX interacts with Bcl-2, which was verified by immunoprecipitation; this interaction is superior after 24 h of CO treatment. Furthermore, CO enhanced Bcl-2 expression in astrocytes. By silencing Bcl-2 expression with siRNA transfection, CO effects in astrocytes were prevented, namely: (i) inhibition of apoptosis, (ii) increase on ATP generation, (iii) stimulation of COX activity, and (iv) mitochondrial biogenesis. Thus, Bcl-2 expression is crucial for CO modulation of oxidative metabolism and for conferring cytoprotection. In conclusion, CO protects astrocytes against oxidative stress-induced apoptosis by improving metabolism functioning, particularly mitochondrial oxidative phosphorylation.

Carbon monoxide induces a late preconditioning-mimetic cardioprotective and antiapoptotic milieu in the myocardium

A growing body of evidence indicates that carbon monoxide (CO), once perceived merely as a poisonous gas, exerts antiapoptotic and cytoprotective effects. Using a water-soluble CO-releasing molecule (CORM) tricarbonylchloro(glycinato)ruthenium(II) (CORM-3), we previously reported that CO induces a delayed protection against myocardial infarction similar to that observed in the late phase of ischemic preconditioning (PC). In the current study, we investigated the molecular mechanisms underlying this cardioprotective effect. The impact on apoptotic signaling pathways was first examined in the setting of ischemia/reperfusion injury. Mice were pretreated with CORM-3 or iCORM-3 (which does not release CO) and subjected to coronary occlusion/reperfusion 24h later. In mice that received CORM-3, there was a significant reduction in markers of apoptosis (cleaved lamin A, cleaved caspase-3, and cleaved PARP-1) after ischemia/reperfusion injury. To elucidate the mechanism of CORM-3-induced cardioprotection we further examined the activation of transcription factors and induction of cardioprotective and apoptosis modulating proteins. Infusion of CORM-3 rapidly activated the stress-responsive transcription factors nuclear factor kappaB (NF-κB), signal transducers and activators of transcription (STAT)1, STAT3, and NF-E2-related factor-2 (Nrf2). This was followed 24h later by upregulation of cardioprotective proteins (heme oxygenase-1 [HO-1], cyclooxygenase-2 [COX-2], and extracellular superoxide dismutase [Ec-SOD]) and antiapoptotic proteins involving both the mitochondria-mediated (Mcl-1) and the death receptor-mediated (c-FLIP(S) and c-FLIP(L)) apoptosis pathways. We conclude that CO released by CORM-3 triggers a cardioprotective signaling cascade that recruits the transcription factors NF-κB, STAT1/3, and Nrf2 with a subsequent increase in cardioprotective and antiapoptotic molecules in the myocardium leading to the late PC-mimetic infarct-sparing effects. This article is part of a Special Issue entitled 'Possible Editorial'.