Carbon monoxide targeting mitochondria

Carbon monoxide and mitochondria: Cell energy and fate control

Carbon monoxide (CO) is a ubiquitously produced endogenous gas in mammalian cells and is involved in stress response being considered as a cytoprotective and homeostatic factor. In the present review, the underlying mechanisms of CO are discussed, in particular CO's impact on cellular metabolism affecting cell fate and function. One of the principal signaling molecules of CO is reactive oxygen species (ROS), particularly hydrogen peroxide, which is mainly generated at the mitochondrial level. Likewise, CO acts on mitochondria modulating oxidative phosphorylation and mitochondria quality control, namely mitochondrial biogenesis (mitobiogenesis) and mitophagy. Other metabolic pathways are also involved in CO's mode of action such as glycolysis and pentose phosphate pathway. The review ends with some new perspectives on CO Biology research. Carboxyhemoglobin (COHb) formation can also be implicated in the CO mode of action, as well as its potential biological role. Finally, other organelles such as peroxisomes hold the potential to be targeted and modulated by CO.

Carbon Monoxide as a Potential Therapeutic Agent: A Molecular Analysis of Its Safety Profiles

Carbon monoxide (CO) is endogenously produced in mammals, with blood concentrations in the high micromolar range in the hemoglobin-bound form. Further, CO has shown therapeutic effects in various animal models. Despite its reputation as a poisonous gas at high concentrations, we show that CO should have a wide enough safety margin for therapeutic applications. The analysis considers a large number of factors including levels of endogenous CO, its safety margin in comparison to commonly encountered biomolecules or drugs, anticipated enhanced safety profiles when delivered via a noninhalation mode, and the large amount of safety data from human clinical trials. It should be emphasized that having a wide enough safety margin for therapeutic use does not mean that it is benign or safe to the general public, even at low doses. We defer the latter to public health experts. Importantly, this Perspective is written for drug discovery professionals and not the general public.

Visible-Light-Activated Carbon Monoxide Release from Porphyrin-Flavonol Hybrids

We report on porphyrin-flavonol hybrids consisting of a porphyrin antenna and four covalently bound 3-hydroxyflavone (flavonol) groups, which act as highly efficient photoactivatable carbon monoxide (CO)-releasing molecules (photoCORMs). These bichromophoric systems enable activation of the UV-absorbing flavonol chromophore by visible light up to 650 nm and offer precise spatial and temporal control of CO administration. The physicochemical properties of the porphyrin antenna system can also be tuned by inserting a metal cation. Our computational study revealed that the process occurs via endergonic triplet-triplet energy transfer from porphyrin to flavonol and may become feasible thanks to flavonol energy stabilization upon intramolecular proton transfer. This mechanism was also indirectly supported by steady-state and transient absorption spectroscopy techniques. Additionally, the porphyrin-flavonol hybrids were found to be biologically benign. With four flavonol CO donors attached to a single porphyrin chromophore, high CO release yields, excellent uncaging cross sections, low toxicity, and CO therapeutic properties, these photoCORMs offer exceptional potential for their further development and future biological and medical applications.

X-ray-controllable release of carbon monoxide potentiates radiotherapy by ultrastable hybrid nanoreservoirs

Carbon monoxide (CO) exhibits unique abilities in sensitizing cancer radiotherapy (RT). However, the development of a highly stable CO-delivery nanosystem with sustained CO release in tumor tissues and the prevention of CO leakage into normal tissues remains a challenge. Herein, an organic-inorganic hybrid strategy is proposed to create ultrastable CO nanoreservoirs by locking an unstable iron carbonyl (FeCO) prodrug in a stable mesoporous silica matrix. Different from traditional FeCO-loading nanoplatforms, FeCO-bridged nanoreservoirs not only tethered labile FeCO in the framework to prevent unwanted FeCO leakage, but also achieved sustained CO release in response to X-ray and endogenous H2O2. Importantly, FeCO-bridged nanoreservoirs exhibited the sequential release of CO and Fe2+, thereby performing highly efficient chemodynamic therapy. Such a powerful combination of RT, gas therapy, and chemodynamic therapy boosts robust immunogenic cell death, thus enabling the elimination of deeply metastatic colon tumors with minimal side effects. The proposed organic-inorganic hybrid strategy opens a new window for the development of stable nanoreservoirs for the on-demand delivery of unstable gases and provides a feasible approach for the sequential release of CO and metal ions from metal carbonyl complexes.

The Critical Assessment of Oxidative Stress Parameters as Potential Biomarkers of Carbon Monoxide Poisoning

In conventional clinical toxicology practice, the blood level of carboxyhemoglobin is a biomarker of carbon monoxide (CO) poisoning but does not correspond to the complete clinical picture and the severity of the poisoning. Taking into account articles suggesting the relationship between oxidative stress parameters and CO poisoning, it seems reasonable to consider this topic more broadly, including experimental biochemical data (oxidative stress parameters) and patients poisoned with CO. This article aimed to critically assess oxidative-stress-related parameters as potential biomarkers to evaluate the severity of CO poisoning and their possible role in the decision to treat. The critically set parameters were antioxidative, including catalase, 2,2-diphenyl-1-picryl-hydrazyl, glutathione, thiol and carbonyl groups. Our preliminary studies involved patients (n = 82) admitted to the Toxicology Clinical Department of the University Hospital of Jagiellonian University Medical College (Kraków, Poland) during 2015-2020. The poisoning was diagnosed based on medical history, clinical symptoms, and carboxyhemoglobin blood level. Blood samples for carboxyhemoglobin and antioxidative parameters were collected immediately after admission to the emergency department. To evaluate the severity of the poisoning, the Pach scale was applied. The final analysis included a significant decrease in catalase activity and a reduction in glutathione level in all poisoned patients based on the severity of the Pach scale: I°-III° compared to the control group. It follows from the experimental data that the poisoned patients had a significant increase in level due to thiol groups and the 2,2-diphenyl-1-picryl-hydrazyl radical, with no significant differences according to the severity of poisoning. The catalase-to-glutathione and thiol-to-glutathione ratios showed the most important differences between the poisoned patients and the control group, with a significant increase in the poisoned group. The ratios did not differentiate the severity of the poisoning. The carbonyl level was highest in the control group compared to the poisoned group but was not statistically significant. Our critical assessment shows that using oxidative-stress-related parameters to evaluate the severity of CO poisoning, the outcome, and treatment options is challenging.

Hyperbaric oxygen therapy in carbon monoxide poisoning in Moroccan patients

Describe the epidemiological, clinical characteristics of acute carbon monoxide poisoning (COP), and the therapeutic effect of hyperbaric oxygen therapy on patient's clinical outcome. This is the first study in this field in Morocco. It studies retrospectively 309 victims of acute COP with major neurological signs. All patients have been treated with hyperbaric oxygen therapy, and have been admitted by the emergency department of the Mohammed V military training hospital in Rabat, between January 2015 and December 2018. All poisonings were accidental and occurred especially in winter (50%), with a predominance in urban areas (93%). The poisoning was often caused by a non-compliant water heater (91%), multi-causality was in half of the cases, and affected adults and women (mean age: 21 ± 17 years, gender (male:female) 1:1.5. The average admission time to the hyperbaric chamber lasted 9 h 04 min (± 12 h 32 min). Clinical signs were mainly unconsciousness (151 cases), headache (85 cases), vomiting (63 cases), nausea (53 cases), and dizziness (51 cases). All the patients benefitted from hyperbaric oxygen therapy sessions. The clinical outcome was positive in the majority of cases, but 23% of the cases presented minor or major sequelae. Patients with sequelae had a longer length of admission than those who had not. COP is a major public health problem in Morocco. Through this study, we suggest the interest of hyperbaric oxygen therapy, especially when it is administered timely without delay.

Carbon monoxide mechanism of protection against renal ischemia and reperfusion injury

Carbon monoxide is quickly moving past its historic label as a molecule once feared, to a therapeutic drug that modulates inflammation. The development of carbon monoxide releasing molecules and utilization of heme oxygenase-1 inducers have shown carbon monoxide to be a promising therapy in reducing renal ischemia and reperfusion injury and other inflammatory diseases. In this review, we will discuss the developments and application of carbon monoxide releasing molecules in renal ischemia and reperfusion injury, and transplantation. We will review the anti-inflammatory mechanisms of carbon monoxide in respect to mitigating apoptosis, suppressing dendritic cell maturation and signalling, inhibiting toll-like receptor activation, promoting anti-inflammatory responses, and the effects on renal vasculature.

Systematic review and meta-analysis of studies between short-term exposure to ambient carbon monoxide and non-accidental, cardiovascular, and respiratory mortality in China

Although a growing number of original epidemiological studies imply a link between ambient pollution exposure and mortality risk, the findings associated with carbon monoxide (CO) exposure are inconsistent. Thus, we conducted a systematic review and meta-analysis of epidemiological studies to evaluate the correlations between ambient CO and non-accidental, cardiovascular, and respiratory mortality in China. Eight databases were searched from inception to 15 May 2021. A random-effect model was used to calculate the pooled relative risks (RRs) and 95% confidence intervals (CIs). Subgroup analyses as well as sensitivity analyses were performed. The I square value (I²) was used to assess heterogeneity among different studies. The assessment of publication bias on included studies was examined by funnel plot and Egger's test. The influence of a potential publication bias on findings was explored by using the trim-and-fill procedure. Ultimately, a total of 19 studies were included in our analysis. The pooled relative risk for each 1 mg/m³ increase of ambient carbon monoxide was 1.0220 (95%CI: 1.0102-1.0339) for non-accidental mortality, 1.0304 (95%CI:1.0154-1.0457) for cardiovascular mortality, and 1.0318 (95%CI:1.0132-1.0506) for respiratory mortality. None of subgroup analyses could explain the source of heterogeneity. Exclusion of any single study did not materially alter the pooled effect estimates. Although it was suggestive of publication bias, findings were generally similar with principal findings when we explored the influence of a potential publication bias using the trim-and-fill method. Our meta-analysis demonstrated that exposure to ambient CO was positive with risk of deaths from all non-accidental causes, total cardiovascular, and respiratory diseases. Based on these findings, tougher intervention policies and initiatives to reduce the health effects of CO exposure should be established.

Carbon Monoxide Inhibits Cytochrome P450 Enzymes CYP3A4/2C8 in Human Breast Cancer Cells, Increasing Sensitivity to Paclitaxel

Paclitaxel (PTX) is a first-line treatment in breast cancer, though resistance develops quickly and frequently. Cytochrome P450 enzymes CYP3A4 and CYP2C8, which metabolically inactivate PTX in hepatic tissue, are overexpressed in malignant breast tissues. CYP3A4 expression correlates with PTX therapy failure and poor outcomes, though no direct evidence of CYP3A4 contributing to PTX sensitivity exists. Because CYP3A4/2C8 is susceptible to carbon monoxide (CO)-mediated inhibition and CO (a gaseous signaling molecule) has previously exhibited drug-sensitizing effects in cancer cells, we hypothesized that CO-mediated inhibition of CYP3A4/2C8 could lead to enhanced drug sensitivity. Using a photo-activated CO-releasing molecule, we have assessed the ability of CO to alter the pharmacokinetics of PTX in breast cancer cells via inhibition of CYP3A4/2C8 and determined that CO does enhance sensitivity of breast cancer cells to PTX. Inhibition of CYP3A4/2C8 by CO could therefore be a promising therapeutic strategy to enhance PTX response in breast cancer.

Carbon monoxide exposure activates ULK1 via AMPK phosphorylation in murine embryonic fibroblasts

Carbon monoxide (CO) is endogenously produced upon degradation of heme by heme oxygenases (HOs) and is suggested to act as a gaseous signaling molecule. The expression of HO-1 is triggered by the Nrf2-Keap1 signaling pathway which responds to exogenous stress signals and dietary constituents such as flavonoids and glucosinolates or reactive metabolic intermediates like 4-hydroxynonenal. Endogenous CO affects energy metabolism, regulates the utilization of glucose and addresses CYP450 enzymes. Using the CO releasing molecule-401 (CORM-401), we studied the effect of endogenous CO on ATP synthesis, AMP-signaling and activation of the AMPK pathway in cell culture. Upon exposure of cells to CORM-401, the mitochondrial ATP production rate was significantly decreased (P=0.007) to about 50%, while glycolytic ATP synthesis was unchanged (P=0.489). Total ATP levels were less affected as determined by mass spectrometry. Instead, levels of ADP and AMP were elevated following CORM-401 exposure by about two- (P=0.022) and four-fold (P=0.012) compared to control, respectively. Increased concentrations of AMP activate AMPK which was demonstrated by a 10 to 15-fold increased phosphorylation of Thr172 of the α-subunit of AMPK (P=0.025). A downstream target of AMPK is the kinase ULK1 which triggers autophagic and mitophagic processes. Activation of ULK1 after CO exposure was proven by a 3 to 5-fold elevated phosphorylation of ULK1 at Ser555 (P=0.004). The present data suggest that production of endogenous CO leads to increasing amounts of AMP which mediates AMPK-dependent downstream effects and likely triggers autophagic processes. Since dietary constituents and their metabolites induce the expression of the CO producing enzyme HO-1, CO signaling may also be involved in the cellular response to nutritional factors.

Heme Oxygenase-1 Signaling and Redox Homeostasis in Physiopathological Conditions

Heme-oxygenase is the enzyme responsible for degradation of endogenous iron protoporphyirin heme; it catalyzes the reaction’s rate-limiting step, resulting in the release of carbon monoxide (CO), ferrous ions, and biliverdin (BV), which is successively reduced in bilirubin (BR) by biliverdin reductase. Several studies have drawn attention to the controversial role of HO-1, the enzyme inducible isoform, pointing out its implications in cancer and other diseases development, but also underlining the importance of its antioxidant activity. The contribution of HO-1 in redox homeostasis leads to a relevant decrease in cells oxidative damage, which can be reconducted to its cytoprotective effects explicated alongside other endogenous mechanisms involving genes like TIGAR (TP53-induced glycolysis and apoptosis regulator), but also to the therapeutic functions of heme main transformation products, especially carbon monoxide (CO), which has been shown to be effective on GSH levels implementation sustaining body’s antioxidant response to oxidative stress. The aim of this review was to collect most of the knowledge on HO-1 from literature, analyzing different perspectives to try and put forward a hypothesis on revealing yet unknown HO-1-involved pathways that could be useful to promote development of new therapeutical strategies, and lay the foundation for further investigation to fully understand this important antioxidant system.

Hemin-decreased cadmium uptake in pak choi (Brassica chinensis L.) seedlings is heme oxygenase-1 dependent and relies on its by-products ferrous iron and carbon monoxide

Cadmium (Cd) is a major pollutant in farmland, which not only greatly restricts crop production, but also brings a serious threat to human health through entering the food chain. Our previous study showed that hemin treatment could reduce the accumulation of Cd in pak choi seedlings. However, the underlying mechanism remains unclear. In this study, we used non-invasive micro-test technology (NMT) to detect the real-time Cd²⁺ flux from pak choi roots and demonstrated that hemin treatment decreased Cd uptake rather than its translocation within plants. Moreover, through comparing the responses of different chemical treatments in pak choi seedlings and Arabidopsis wild-type and heme oxygenase-1 (HO-1) mutant, we provided evidence that hemin-decreased Cd uptake was HO-1 dependent. Furthermore, analyses of hemin degradation products suggested that the hemin-derived suppression of Cd uptake suppression was probably relying on its degradation by-products, ferrous iron (Fe²⁺) and carbon monoxide (CO), via repressing the expression of a Fe²⁺/Cd²⁺ transporter BcIRT1 in pak choi roots.

Mycobacterial Control of Host Mitochondria: Bioenergetic and Metabolic Changes Shaping Cell Fate and Infection Outcome

Mitochondria, are undoubtedly critical organelle of a eukaryotic cell, which provide energy and offer a platform for most of the cellular signaling pathways that decide cell fate. The role of mitochondria in immune-metabolism is now emerging as a crucial process governing several pathological states, including infection, cancer, and diabetes. Mitochondria have therefore been a vulnerable target for several bacterial and viral pathogens to control host machinery for their survival, replication, and dissemination. Mycobacterium tuberculosis, a highly successful human pathogen, persists inside alveolar macrophages at the primary infection site, applying several strategies to circumvent macrophage defenses, including control of host mitochondria. The infection perse and specific mycobacterial factors that enter the host mitochondrial milieu perturb mitochondrial dynamics and function by disturbing mitochondrial membrane potential, shifting bioenergetics parameters such as ATP and ROS, orienting the host cell fate and thereby infection outcome. In the present review, we attempt to integrate the available information and emerging dogmas to get a holistic view of Mycobacterium tuberculosis infection vis-a-vis mycobacterial factors that target host mitochondria and changes therein in terms of morphology, dynamics, proteomic, and bioenergetic alterations that lead to a differential cell fate and immune response determining the disease outcome. We also discuss critical host factors and processes that are overturned by Mycobacterium tuberculosis, such as cAMP-mediated signaling, redox homeostasis, and lipid droplet formation. Further, we also present alternate dogmas as well as the gaps and limitations in understanding some of the present research areas, which can be further explored by understanding some critical processes during Mycobacterium tuberculosis infection and the reasons thereof. Toward the end, we propose to have a set of guidelines for pursuing investigations to maintain uniformity in terms of early and late phase, MOI of infection, infection duration and incubation periods, the strain of mycobacteria, passage numbers, and so on, which all work as probable variables toward different readouts. Such a setup would, therefore, help in the smooth integration of information across laboratories toward a better understanding of the disease and possibilities of host-directed therapy.

Neuroimaging of Propofol Infusion Syndrome: A Case Report and Review of Literature

A school-age boy with a complex medical history underwent a minor elective surgical procedure. Propofol was used for sedation during the procedure. The patient could not be awakened post-operatively. Laboratory findings demonstrated metabolic lactic acidosis, leukocytosis with bandemia, and transaminitis. Neuroimaging demonstrated findings that were consistent with hypoxic-ischemic or toxic-metabolic brain injury involving the bilateral basal ganglia, hippocampi, and cerebellum. The patient's condition progressively worsened over the course of the following few weeks, and brain death was confirmed by scintigraphy seven weeks later. Prompt neuroimaging in unresponsive patients with suspected propofol infusion syndrome (PRIS) is of critical importance in detecting neurologic injuries, excluding alternative diagnoses, and determining prognostication.

Endogenous Carbon Monoxide Signaling Modulates Mitochondrial Function and Intracellular Glucose Utilization: Impact of the Heme Oxygenase Substrate Hemin

Stress-inducible heme oxygenase-1 (HO-1) catalyzes the oxidative cleavage of heme yielding biliverdin, ferrous iron, and carbon monoxide (CO). Heme oxygenase activity has been attributed to antioxidant defense via the redox cycling system of biliverdin and bilirubin. There is increasing evidence that CO is a gaseous signaling molecule and plays a role in the regulation of energy metabolism. Inhibitory effects of CO on the respiratory chain are well established, but the implication of such a process on the cellular stress response is not well understood. By means of extracellular flux analyses and isotopic tracing, we studied the effects of CO, either released from the CO donor CORM-401 or endogenously produced by heme oxygenases, on the respiratory chain and glucose metabolism. CORM-401 was thereby used as a tool to mimic endogenous CO production by heme oxygenases. In the long term (>60 min), CORM-401-derived CO exposure inhibited mitochondrial respiration, which was compensated by increased glycolysis accompanied by a loss of the ATP production rate and an increase in proton leakage. This effect pattern was likewise observed after endogenous CO production by heme oxygenases. However, in the present setting, these effects were only observed when sufficient substrate for heme oxygenases (hemin) was provided. Modulation of the HO-1 protein level was less important. The long-term influence of CO on glucose metabolism via glycolysis was preceded by a short-term response (<30 min) of the cells to CO. Stable isotope-labeling experiments and metabolic flux analysis revealed a short-term shift of glucose consumption from glycolysis to the pentose phosphate pathway (PPP) along with an increase in reactive oxygen species (ROS) generation. Overall, we suggest that signaling by endogenous CO stimulates the rapid formation of reduction equivalents (NADPH) via the PPP, and plays an additional role in antioxidant defense, e.g., via feed-forward stimulation of the bilirubin/biliverdin redox cycling system.

Targeting the Heme Oxygenase 1/Carbon Monoxide Pathway to Resolve Lung Hyper-Inflammation and Restore a Regulated Immune Response in Cystic Fibrosis

In individuals with cystic fibrosis (CF), lung hyper-inflammation starts early in life and is perpetuated by mucus obstruction and persistent bacterial infections. The continuous tissue damage and scarring caused by non-resolving inflammation leads to bronchiectasis and, ultimately, respiratory failure. Macrophages (MΦs) are key regulators of immune response and host defense. We and others have shown that, in CF, MΦs are hyper-inflammatory and exhibit reduced bactericidal activity. Thus, MΦs contribute to the inability of CF lung tissues to control the inflammatory response or restore tissue homeostasis. The non-resolving hyper-inflammation in CF lungs is attributed to an impairment of several signaling pathways associated with resolution of the inflammatory response, including the heme oxygenase-1/carbon monoxide (HO-1/CO) pathway. HO-1 is an enzyme that degrades heme groups, leading to the production of potent antioxidant, anti-inflammatory, and bactericidal mediators, such as biliverdin, bilirubin, and CO. This pathway is fundamental to re-establishing cellular homeostasis in response to various insults, such as oxidative stress and infection. Monocytes/MΦs rely on abundant induction of the HO-1/CO pathway for a controlled immune response and for potent bactericidal activity. Here, we discuss studies showing that blunted HO-1 activation in CF-affected cells contributes to hyper-inflammation and defective host defense against bacteria. We dissect potential cellular mechanisms that may lead to decreased HO-1 induction in CF cells. We review literature suggesting that induction of HO-1 may be beneficial for the treatment of CF lung disease. Finally, we discuss recent studies highlighting how endogenous HO-1 can be induced by administration of controlled doses of CO to reduce lung hyper-inflammation, oxidative stress, bacterial infection, and dysfunctional ion transport, which are all hallmarks of CF lung disease.

Heme is required for carbon monoxide activation of mitochondrial BKCa channel

Carbon monoxide (CO) is an endogenously synthesized gaseous mediator and is involved in the regulation of numerous physiological processes. Mitochondria, in which hemoproteins are abundant, are among the targets for CO action. Large-conductance calcium-activated (mitoBK_Ca) channels in the inner mitochondrial membrane share multiple biophysical similarities with the BK_Ca channels of the plasma membrane and could be a potential target for CO. To test this hypothesis, the activity of the mitoBK_Ca channels in human astrocytoma U-87 MG cell mitochondria was assessed with the patch-clamp technique. The effects of CO-releasing molecules (CORMs), such as CORM-2, CORM-401, and CORM-A1, were compared to the application of a CO-saturated solution to the mitoBK_Ca channels in membrane patches. The applied CORMs showed pleiotropic effects including channel inhibition, while the CO-containing solution did not significantly modulate channel activity. Interestingly, CO applied to the mitoBK_Ca channels, which were inhibited by exogenously added heme, stimulated the channel. To summarize, our findings indicate a requirement of heme binding to the mitoBK_Ca channel for channel modulation by CO and suggest that CORMs might have complex unspecific effects on mitoBK_Ca channels.

A multistage assembly/disassembly strategy for tumor-targeted CO delivery

CO gas molecule not only could selectively kill cancer cells but also exhibits limited anticancer efficacy because of the lack of active tumor-targeted accumulation capability. In this work, a multistage assembly/disassembly strategy is developed to construct a new intelligent nanomedicine by encapsulating a mitochondria-targeted and intramitochondrial microenvironment-responsive prodrug (FeCO-TPP) within mesoporous silica nanoparticle that is further coated with hyaluronic acid by step-by-step electrostatic assembly, realizing tumor tissue-cell-mitochondria-targeted multistage delivery and controlled release of CO in a step-by-step disassembly way. Multistage targeted delivery and controlled release of CO involve (i) the passive tumor tissue-targeted nanomedicine delivery, (ii) the active tumor cell-targeted nanomedicine delivery, (iii) the acid-responsive prodrug release, (iv) the mitochondria-targeted prodrug delivery, and (v) the ROS-responsive CO release. The developed nanomedicine has effectively augmented the efficacy and safety of CO therapy of cancer both in vitro and in vivo. The proposed multistage assembly/disassembly strategy opens a new window for targeted CO therapy.

CO-mediated cytoprotection is dependent on cell metabolism modulation

Carbon monoxide (CO) is a gasotransmitter endogenously produced by the activity of heme oxygenase, which is a stress-response enzyme. Endogenous CO or low concentrations of exogenous CO have been described to present several cytoprotective functions: anti-apoptosis, anti-inflammatory, vasomodulation, maintenance of homeostasis, stimulation of preconditioning and modulation of cell differentiation. The present review revises and discuss how CO regulates cell metabolism and how it is involved in the distinct cytoprotective roles of CO. The first found metabolic effect of CO was its increase on cellular ATP production, and since then much data have been generated. Mitochondria are the most described and studied cellular targets of CO. Mitochondria exposure to this gasotransmitter leads several consequences: ROS generation, stimulation of mitochondrial biogenesis, increased oxidative phosphorylation or mild uncoupling effect. Likewise, CO negatively regulates glycolysis and improves pentose phosphate pathway. More recently, CO has also been disclosed as a regulating molecule for metabolic diseases, such as obesity and diabetes with promising results.

High-Sensitivity Troponin I and Creatinine Kinase-Myocardial Band in Screening for Myocardial Injury in Patients with Carbon Monoxide Poisoning

Myocardial dysfunction due to acute carbon monoxide (CO) poisoning is common and associated with poor outcomes. The role of cardiac markers, including creatine kinase-myocardial band (CK-MB), high-sensitivity troponin I (hsTnI), and brain natriuretic peptide (BNP), in identifying patients with CO-induced cardiomyopathy were evaluated. This single-center, retrospective cohort study included 905 consecutive adult patients in the CO poisoning registry from February 2009 to December 2019. Cardiomyopathy was defined as any abnormality on transthoracic echocardiography (TTE), including left ventricular systolic and diastolic dysfunction, right ventricular dysfunction, and wall motion abnormalities. The areas under receiver operating curves (AUCs) for biomarkers were compared. Of the 850 included patients, 101 (11.9%) had CO-induced cardiomyopathy. Initial and peak hsTnI and CK-MB concentrations, and initial BNP concentrations were significantly higher in patients with than without cardiomyopathy (all P-values < 0.01), but the AUCs were higher for hsTnI (0.894) and CK-MB (0.864) than for BNP (0.796). Initial TnI > 0.01 ng/mL and CK-MB > 1.5 ng/mL each had 95% sensitivity and 97% negative predictive value for CO-induced cardiomyopathy. Higher hsTnI or CK-MB levels on admission can identify patients at high-risk of CO-induced cardiomyopathy and can be a screening tool for CO poisoning.

The compensatory antioxidant response system with a focus on neuroprogressive disorders

Major antioxidant responses to increased levels of inflammatory, oxidative and nitrosative stress (ONS) are detailed. In response to increasing levels of nitric oxide, S-nitrosylation of cysteine thiol groups leads to post-transcriptional modification of many cellular proteins and thereby regulates their activity and allows cellular adaptation to increased levels of ONS. S-nitrosylation inhibits the function of nuclear factor kappa-light-chain-enhancer of activated B cells, toll-like receptor-mediated signalling and the activity of several mitogen-activated protein kinases, while activating nuclear translocation of nuclear factor (erythroid-derived 2)-like 2 (Nrf2 or NFE2L2); in turn, the redox-regulated activation of Nrf2 leads to increased levels and/or activity of key enzymes and transporter systems involved in the glutathione system. The Nrf2/Kelch-like ECH-associated protein-1 axis is associated with upregulation of NAD(P)H:quinone oxidoreductase 1, which in turn has anti-inflammatory effects. Increased Nrf2 transcriptional activity also leads to activation of haem oxygenase-1, which is associated with upregulation of bilirubin, biliverdin and biliverdin reductase as well as increased carbon monoxide signalling, anti-inflammatory and antioxidant activity. Associated transcriptional responses, which may be mediated by retrograde signalling owing to elevated hydrogen peroxide, include the unfolded protein response (UPR), mitohormesis and the mitochondrial UPR; the UPR also results from increasing levels of mitochondrial and cytosolic reactive oxygen species and reactive nitrogen species leading to nitrosylation, glutathionylation, oxidation and nitration of crucial cysteine and tyrosine causing protein misfolding and the development of endoplasmic reticulum stress. It is shown how these mechanisms co-operate in forming a co-ordinated rapid and prolonged compensatory antioxidant response system.

Prognostic factors of carbon monoxide poisoning in Taiwan: a retrospective observational study

OBJECTIVES

To identify the risk factors related to the prognosis of carbon monoxide (CO)-poisoned patients in the hospital.

DESIGN

Retrospective observational study.

SETTING

Tri-Service General Hospital, Taiwan.

METHODS

We conducted a review of the medical records of 669 CO-poisoned patients, who were admitted to the Department of Emergency, Tri-Service General Hospital, Taiwan, from 2009 to 2014. Demographic, clinical and laboratory data were collected for analysis. In the study, the end points for poor outcome were patients who either still had sequelae, were bedridden or died after treatment. The independent t-test, χ² test and binary logistic regression were used to identify the association between the prognostic factors and the outcomes.

RESULTS

The logistic regression analysis confirmed that the Glasgow Coma Scale (GCS) score (p=0.008) and blood urea nitrogen (BUN) (p=0.002) were related to poor outcomes. Furthermore, the receiver operating characteristic (ROC) curve showed that the cut-off point of intubation days was 1.5 days (area under the ROC curve [AUC]=0.793) for all patients and 2.5 days (AUC=0.817) for patients with intubation when predicting poor outcomes.

CONCLUSION

We identified the factors that most strongly predict the prognosis of CO poisoning, including the GCS score, serum BUN and intubation days. Moreover, the number of hyperbaric oxygen treatments seems to have impact of the outcome.

Carbon Monoxide Partially Mediates Protective Effect of Resveratrol Against UVB-Induced Oxidative Stress in Human Keratinocytes

Based on the antioxidative effect of resveratrol (RES) in mitigating reactive oxygen species (ROS) production through the induction of nuclear factor-erythroid 2-related factor-2 (Nrf2)/heme oxigenase-1 (HO-1) signaling pathway, we investigated whether the protective activity of RES against ROS-mediated cytotoxicity is mediated by intracellular carbon monoxide (CO), a product of HO-1 activity, in ultraviolet B (UVB)-irradiated human keratinocyte HaCaT cells. The cells were exposed to UVB radiation following treatment with RES and/or CO-releasing molecule-2 (CORM-2). RES and/or CORM-2 upregulated HO-1 protein expression, accompanied by a gradual reduction of UVB-induced intracellular ROS levels. CORM-2 reduced intracellular ROS in the presence of tin protoporphyrin IX, an HO-1 inhibitor, indicating that the cytoprotection observed was mediated by intracellular CO and not by HO-1 itself. Moreover, CORM-2 decreased RES-stimulated mitochondrial quantity and respiration and increased the cytosolic protein expressions of radical-scavenging superoxide dismutases, SOD1 and SOD2. Taken together, our observations suggest that RES and intracellular CO act independently, at least partly, in attenuating cellular oxidative stress by promoting antioxidant enzyme expressions and inhibiting mitochondrial respiration in UVB-exposed keratinocytes.

Therapeutic effect of carbon monoxide-releasing molecule-3 on acute lung injury after hemorrhagic shock and resuscitation

Hemorrhagic shock and resuscitation (HSR) induces a pulmonary inflammatory response and frequently causes acute lung injury. Carbon monoxide-releasing molecule-3 (CORM-3) has been reported to liberate and deliver CO under physiological conditions, which exerts organ-protective effects during systemic insults. The present study aimed to determine whether the administration of CORM-3 following HSR exerts a therapeutic effect against HSR-induced lung injury without any detrimental effects on oxygenation and hemodynamics. To induce hemorrhagic shock, rats were bled to a mean arterial blood pressure of 30 mmHg for 45 min and then resuscitated with the shed blood. CORM-3 or a vehicle was intravenously administered immediately following the completion of resuscitation. The rats were divided into four groups, including sham, HSR, HSR/CORM-3 and HSR/inactive CORM-3 groups. Arterial blood gas parameters and vital signs were recorded during HSR. The histopathological changes to the lungs were evaluated using a lung injury score, while pulmonary edema was evaluated on the basis of the protein concentration in bronchoalveolar lavage fluid and the lung wet/dry ratio. We also investigated the pulmonary expression levels of inflammatory mediators and apoptotic markers such as cleaved caspase-3 and transferase-mediated dUTP-fluorescein isothiocyanate nick-end labeling (TUNEL) staining. Although HSR caused significant lung histopathological damage and pulmonary edema, CORM-3 significantly ameliorated this damage. CORM-3 also attenuated the HSR-induced upregulation of tumor necrosis factor-α, inducible nitric oxide synthase and interleukin-1β genes, and the expression of interleukin-1β and macrophage inflammatory protein-2. In addition, the expression of interleukin-10, an anti-inflammatory cytokine, was inversely enhanced by CORM-3, which also reduced the number of TUNEL-positive cells and the expression of cleaved caspase-3 following HSR. Although CORM-3 was administered during the acute phase of HSR, it did not exert any influence on arterial blood gas analysis data and vital signs during HSR. Therefore, treatment with CORM-3 ameliorated HSR-induced lung injury, at least partially, through anti-inflammatory and anti-apoptotic effects, without any detrimental effects on oxygenation and hemodynamics.

Neurointegrity and neurophysiology: astrocyte, glutamate, and carbon monoxide interactions

Astrocyte contributions to brain function and prevention of neuropathologies are as extensive as that of neurons. Astroglial regulation of glutamate, a primary neurotransmitter, is through uptake, release through vesicular and non-vesicular pathways, and catabolism to intermediates. Homeostasis by astrocytes is considered to be of primary importance in determining normal central nervous system health and central nervous system physiology - glutamate is central to dynamic physiologic changes and central nervous system stability. Gasotransmitters may affect diverse glutamate interactions positively or negatively. The effect of carbon monoxide, an intrinsic central nervous system gasotransmitter, in the complex astrocyte homeostasis of glutamate may offer insights to normal brain development, protection, and its use as a neuromodulator and neurotherapeutic. In this article, we will review the effects of carbon monoxide on astrocyte homeostasis of glutamate.

Mitochondrial-Localized Versus Cytosolic Intracellular CO-Releasing Organic PhotoCORMs: Evaluation of CO Effects Using Bioenergetics

While interactions between carbon monoxide (CO) and mitochondria have been previously studied, the methods used to deliver CO (gas or CO-releasing metal carbonyl compounds) lack subcellular targeting and/or controlled delivery. Thus, the effective concentration needed to produce changes in mitochondrial bioenergetics is yet to be fully defined. To evaluate the influence of mitochondrial-targeted versus intracellularly released CO on mitochondrial oxygen consumption rates, we developed and characterized flavonol-based CO donor compounds that differ at their site of release. These molecules are metal-free, visible light triggered CO donors (photoCORMs) that quantitatively release CO and are trackable in cells via confocal microscopy. Our studies indicate that at a concentration of 10 μM, the mitochondrial-localized and cytosolic CO-releasing compounds are similarly effective in terms of decreasing ATP production, maximal respiration, and the reserve capacity of A549 cells. This concentration is the lowest to impart changes in mitochondrial bioenergetics for any CO-releasing molecule (CORM) reported to date. The results reported herein demonstrate the feasibility of using a structurally tunable organic photoCORM framework for comparative intracellular studies of the biological effects of carbon monoxide.

Therapeutic Aspects of Carbon Monoxide in Cardiovascular Disease

Carbon monoxide (CO) is being increasingly recognized as a potential therapeutic with important signaling functions in various diseases. Carbon monoxide-releasing molecules (CORMs) show anti-apoptotic, anti-inflammatory, and anti-oxidant effects on the tissues of organisms, thus contributing to tissue homeostasis. An increase in reactive oxygen species production from the mitochondria after exposure to CO is also considered one of the underlying mechanisms of cardioprotection, although mitochondrial inhibition is the main toxic mechanism of CO poisoning. This review highlights the mechanism of the biological effects of CO and its potential application as a therapeutic in clinical settings, including in cardiovascular diseases. This review also discusses the obstacles and limitations of using exogenous CO or CORMs as a therapeutic option, with respect to acute CO poisoning.

Macrophages are exploited from an innate wound healing response to facilitate cancer metastasis

Tumour-associated macrophages (TAMs) play an important role in tumour progression, which is facilitated by their ability to respond to environmental cues. Here we report, using murine models of breast cancer, that TAMs expressing fibroblast activation protein alpha (FAP) and haem oxygenase-1 (HO-1), which are also found in human breast cancer, represent a macrophage phenotype similar to that observed during the wound healing response. Importantly, the expression of a wound-like cytokine response within the tumour is clinically associated with poor prognosis in a variety of cancers. We show that co-expression of FAP and HO-1 in macrophages results from an innate early regenerative response driven by IL-6, which both directly regulates HO-1 expression and licenses FAP expression in a skin-like collagen-rich environment. We show that tumours can exploit this response to facilitate transendothelial migration and metastatic spread of the disease, which can be pharmacologically targeted using a clinically relevant HO-1 inhibitor.

Improvement of neuronal differentiation by carbon monoxide: Role of pentose phosphate pathway

Over the last decades, the silent-killer carbon monoxide (CO) has been shown to also be an endogenous cytoprotective molecule able to inhibit cell death and modulate mitochondrial metabolism. Neuronal metabolism is mostly oxidative and neurons also use glucose for maintaining their anti-oxidant status by generation of reduced glutathione (GSH) via the pentose-phosphate pathway (PPP). It is established that neuronal differentiation depends on reactive oxygen species (ROS) generation and signalling, however there is a lack of information about modulation of the PPP during adult neurogenesis. Thus, the main goal of this study was to unravel the role of CO on cell metabolism during neuronal differentiation, particularly by targeting PPP flux and GSH levels as anti-oxidant system. A human neuroblastoma SH-S5Y5 cell line was used, which differentiates into post-mitotic neurons by treatment with retinoic acid (RA), supplemented or not with CO-releasing molecule-A1 (CORM-A1). SH-SY5Y cell differentiation supplemented with CORM-A1 prompted an increase in neuronal yield production. It did, however, not alter glycolytic metabolism, but increased the PPP. In fact, CORM-A1 treatment stimulated (i) mRNA expression of 6-phosphogluconate dehydrogenase (PGDH) and transketolase (TKT), which are enzymes for oxidative and non-oxidative phases of the PPP, respectively and (ii) protein expression and activity of glucose 6-phosphate dehydrogenase (G6PD) the rate-limiting enzyme of the PPP. Likewise, whenever G6PD was knocked-down CO-induced improvement on neuronal differentiation was reverted, while pharmacological inhibition of GSH synthesis did not change CO's effect on the improvement of neuronal differentiation. Both results indicate the key role of PPP in CO-modulation of neuronal differentiation. Furthermore, at the end of SH-SY5Y neuronal differentiation process, CORM-A1 supplementation increased the ratio of reduced and oxidized glutathione (GSH/GSSG) without alteration of GSH metabolism. These data corroborate with PPP stimulation. In conclusion, CO improves neuronal differentiation of SH-S5Y5 cells by stimulating the PPP and modulating the GSH system.

Enrichment-triggered prodrug activation demonstrated through mitochondria-targeted delivery of doxorubicin and carbon monoxide

Controlled activation is a critical component in prodrug development. Here we report a concentration-sensitive platform approach for bioorthogonal prodrug activation by taking advantage of reaction kinetics. Using two 'click and release' systems, we demonstrate enrichment and prodrug activation specifically in mitochondria to demonstrate the principle of the approach. In both cases, the payload (doxorubicin or carbon monoxide) was released inside the mitochondrial matrix following the enrichment-initiated click reaction. Furthermore, mitochondria-targeted delivery yielded substantial augmentation of functional biological and therapeutic effects in vitro and in vivo when compared to controls, which did not result in enrichment. This method is thus a platform for targeted drug delivery that is amenable to conjugation with a variety of molecules and is not limited to cell-surface delivery. Taken together, these two 'click and release' pairs clearly demonstrate the concept of enrichment-triggered drug release and the critical feasibility of treating clinically relevant diseases such as acute liver injury and cancer.

Intermittent, low dose carbon monoxide exposure enhances survival and dopaminergic differentiation of human neural stem cells

Exploratory studies using human fetal tissue have suggested that intrastriatal transplantation of dopaminergic neurons may become a future treatment for patients with Parkinson's disease. However, the use of human fetal tissue is compromised by ethical, regulatory and practical concerns. Human stem cells constitute an alternative source of cells for transplantation in Parkinson's disease, but efficient protocols for controlled dopaminergic differentiation need to be developed. Short-term, low-level carbon monoxide (CO) exposure has been shown to affect signaling in several tissues, resulting in both protection and generation of reactive oxygen species. The present study investigated the effect of CO produced by a novel CO-releasing molecule on dopaminergic differentiation of human neural stem cells. Short-term exposure to 25 ppm CO at days 0 and 4 significantly increased the relative content of β-tubulin III-immunoreactive immature neurons and tyrosine hydroxylase expressing catecholaminergic neurons, as assessed 6 days after differentiation. Also the number of microtubule associated protein 2-positive mature neurons had increased significantly. Moreover, the content of apoptotic cells (Caspase3) was reduced, whereas the expression of a cell proliferation marker (Ki67) was left unchanged. Increased expression of hypoxia inducible factor-1α and production of reactive oxygen species (ROS) in cultures exposed to CO may suggest a mechanism involving mitochondrial alterations and generation of ROS. In conclusion, the present procedure using controlled, short-term CO exposure allows efficient dopaminergic differentiation of human neural stem cells at low cost and may as such be useful for derivation of cells for experimental studies and future development of donor cells for transplantation in Parkinson's disease.

Hypometabolism as the ultimate defence in stress response: how the comparative approach helps understanding of medically relevant questions

First conceptualized from breath-hold diving mammals, later recognized as the ultimate cell autonomous survival strategy in anoxia-tolerant vertebrates and burrowing or hibernating rodents, hypometabolism is typically recruited by resilient organisms to withstand and recover from otherwise life-threatening hazards. Through the coordinated down-regulation of biosynthetic, proliferative and electrogenic expenditures at times when little ATP can be generated, a metabolism turned 'down to the pilot light' allows the re-balancing of energy demand with supply at a greatly suppressed level in response to noxious exogenous stimuli or seasonal endogenous cues. A unifying hallmark of stress-tolerant organisms, the adaptation effectively prevents lethal depletion of ATP, thus delineating a marked contrast with susceptible species. Along with disengaged macromolecular syntheses, attenuated transmembrane ion shuttling and PO₂ -conforming respiration rates, the metabolic slowdown in tolerant species usually culminates in a non-cycling, quiescent phenotype. However, such a reprogramming also occurs in leading human pathophysiologies. Ranging from microbial infections through ischaemia-driven infarcts to solid malignancies, cells involved in these disorders may again invoke hypometabolism to endure conditions non-permissive for growth. At the same time, their reduced activities underlie the frequent development of a general resistance to therapeutic interventions. On the other hand, a controlled induction of hypometabolic and/or hypothermic states by pharmacological means has recently stimulated intense research aimed at improved organ preservation and patient survival in situations requiring acutely administered critical care. The current review article therefore presents an up-to-date survey of concepts and applications of a coordinated and reversibly down-regulated metabolic rate as the ultimate defence in stress responses.

TGFβ-Responsive HMOX1 Expression Is Associated with Stemness and Invasion in Glioblastoma Multiforme

Glioblastoma multiforme (GBM) is the most common and lethal adult brain tumor. Resistance to standard radiation and chemotherapy is thought to involve survival of GBM cancer stem cells (CSCs). To date, no single marker for identifying GBM CSCs has been able to capture the diversity of CSC populations, justifying the needs for additional CSC markers for better characterization. Employing targeted mass spectrometry, here we present five cell-surface markers HMOX1, SLC16A1, CADM1, SCAMP3, and CLCC1 which were found to be elevated in CSCs relative to healthy neural stem cells (NSCs). Transcriptomic analyses of REMBRANDT and TCGA compendiums also indicated elevated expression of these markers in GBM relative to controls and non-GBM diseases. Two markers SLC16A1 and HMOX1 were found to be expressed among pseudopalisading cells that reside in the hypoxic region of GBM, substantiating the histopathological hallmarks of GBM. In a prospective study (N = 8) we confirmed the surface expression of HMOX1 on freshly isolated primary GBM cells (P0). Employing functional assays that are known to evaluate stemness, we demonstrate that elevated HMOX1 expression is associated with stemness in GBM and can be modulated through TGFβ. siRNA-mediated silencing of HMOX1 impaired GBM invasion-a phenomenon related to poor prognosis. In addition, surgical resection of GBM tumors caused declines (18% ± 5.1SEM) in the level of plasma HMOX1 as measured by ELISA, in 8/10 GBM patients. These findings indicate that HMOX1 is a robust predictor of GBM CSC stemness and pathogenesis. Further understanding of the role of HMOX1 in GBM may uncover novel therapeutic approaches. Stem Cells 2016;34:2276-2289.

Carbon monoxide improves neuronal differentiation and yield by increasing the functioning and number of mitochondria

The process of cell differentiation goes hand-in-hand with metabolic adaptations, which are needed to provide energy and new metabolites. Carbon monoxide (CO) is an endogenous cytoprotective molecule able to inhibit cell death and improve mitochondrial metabolism. Neuronal differentiation processes were studied using the NT2 cell line, which is derived from human testicular embryonic teratocarcinoma and differentiates into post-mitotic neurons upon retinoic acid treatment. CO-releasing molecule A1 (CORM-A1) was used do deliver CO into cell culture. CO treatment improved NT2 neuronal differentiation and yield, since there were more neurons and the total cell number increased following the differentiation process. CO supplementation enhanced the mitochondrial population in post-mitotic neurons derived from NT2 cells, as indicated by an increase in mitochondrial DNA. CO treatment during neuronal differentiation increased the extent of the classical metabolic change that occurs during neuronal differentiation, from glycolytic to more oxidative metabolism, by decreasing the ratio of lactate production and glucose consumption. The expression of pyruvate and lactate dehydrogenases was higher, indicating an augmented oxidative metabolism. Moreover, these findings were corroborated by an increased percentage of (13) C incorporation from [U-(13) C]glucose into the tricarboxylic acid cycle metabolites malate and citrate, and also glutamate and aspartate in CO-treated cells. Finally, under low levels of oxygen (5%), which enhances glycolytic metabolism, some of the enhancing effects of CO on mitochondria were not observed. In conclusion, our data show that CO improves neuronal and mitochondrial yield by stimulation of tricarboxylic acid cycle activity, and thus oxidative metabolism of NT2 cells during the process of neuronal differentiation. The process of cell differentiation is coupled with metabolic adaptations. Carbon monoxide (CO) is an endogenous cytoprotective gasotransmitter able to prevent cell death and improve mitochondrial metabolism. Herein CO supplementation improved neuronal differentiation yield, by enhancing mitochondrial population and promoting the classical metabolic change that occurs during neuronal differentiation, from glycolytic to oxidative metabolism.

COHb Level and High-Sensitivity Cardiac Troponin T in 2012 in Bursa, Turkey: A Retrospective Single-Center Study

Background

Intoxication due to carbon monoxide (CO) is one of the most common types of poisoning. Cardiac effects of carboxyhemoglobin (COHb) range from simple arrhythmias to myocardial infarction.

Objectives

The current study aimed to investigate the relationship between blood carboxyhemoglobin and high-sensitivity cardiac troponin T (hs-cTnT) level with a highly sensitive assay in patients with acute carbon monoxide poisoning.

Patients and Methods

This retrospective study was conducted on 141 (54 males and 87 females) patients, with acute CO intoxication, admitted to the Sevket Yilmaz research and education hospital emergency unit during a one-year period (January 2012 - January 2013). The patients were divided into three groups based on COHb levels: Group I, mild COHb level < 15%; Group II, COHb between 15% and 25%; Group III, severe acute CO intoxication COHb levels > 25%. COHb, hs-cTnT (Stat), creatine kinase (CK) and creatine kinase-myocardial band (CK-MB) levels were measured on admission.

Results

The mean age of the patients was 38 ± 16 years. COHb levels ranged from 8 to 35. hs-cTnT levels on inclusion in this study were slightly different between the groups (P = 0.05). COHb levels with hs-cTnT values were weakly correlated (r = 0.173, P = 0.041); on the other hand, CK-MB levels were not correlated with COHb (r = 0.013, P = 0.883).

Conclusions

In patients without clear signs of myocardial infarction, even mild CO poisoning was associated with quantifiable circulating levels of hs-cTnT when TnT was measured using a highly sensitive assay in the current study patients. Plasma levels of the hs-TnT and CK-MB assays were not correlated with the COHb levels in the current study patients.

Effects of carbon monoxide-releasing molecules on pulmonary vasoreactivity in isolated perfused lungs

In addition to its renowned poisonous effects, carbon monoxide (CO) is being recognized for its beneficial actions on inflammatory and vasoregulatory pathways, particularly when applied at low concentrations via CO-releasing molecules (CO-RMs). In the lung, CO gas and CO-RMs are suggested to decrease pulmonary vascular tone and hypoxic pulmonary vasoconstriction (HPV). However, the direct effect of CO-RMs on the pulmonary vasoreactivity in isolated lungs has not yet been investigated. We assessed the effect of CORM-2 and CORM-3 on the pulmonary vasculature during normoxia and acute hypoxia (1% oxygen for 10 min) in isolated ventilated and perfused mouse lungs. The effects were compared with those of inhaled CO gas (10%). The interaction of CORM-2 or CO with cytochrome P-450 (CYP) was measured simultaneously by tissue spectrophotometry. Inhaled CO decreased HPV and vasoconstriction induced by the thromboxane mimetic U-46619 but did not alter KCl-induced vasoconstriction. In contrast, concentrations of CORM-2 and CORM-3 used to elicit beneficial effects on the systemic circulation did not affect pulmonary vascular tone. High concentration of CO-RMs or long-term application induced a continuous increase in normoxic pressure. Inhaled CO showed spectral alterations correlating with the inhibition of CYP. In contrast, during application of CORM-2 spectrophotometric signs of interaction with CYP could not be detected. Application of CO-RMs in therapeutic doses in isolated lungs neither decreases pulmonary vascular tone and HPV nor does it induce spectral alterations that are characteristic of CO-inhibited CYP. High doses, however, may cause pulmonary vasoconstriction.

Molecular basis of reduced birth weight in smoking pregnant women: mitochondrial dysfunction and apoptosis

In utero exposure of fetuses to tobacco is associated with reduced birth weight. We hypothesized that this may be due to the toxic effect of carbon monoxide (CO) from tobacco, which has previously been described to damage mitochondria in non-pregnant adult smokers. Maternal peripheral blood mononuclear cells (PBMCs), newborn cord blood mononuclear cells (CBMCs) and placenta were collected from 30 smoking pregnant women and their newborns and classified as moderate and severe smoking groups, and compared to a cohort of 21 non-smoking controls. A biomarker for tobacco consumption (cotinine) was assessed by ELISA (enzyme-linked immunosorbent assay). The following parameters were measured in all tissues: mitochondrial chain complex IV [cytochrome c oxidase (COX)] activity by spectrophotometry, mitochondrial DNA levels by reverse transcription polymerase chain reaction, oxidative stress by spectrophotometric lipid peroxide quantification, mitochondrial mass through citrate synthase spectrophotometric activity and apoptosis by Western blot parallelly confirmed by TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labelling) assay in placenta. Newborns from smoking pregnant women presented reduced birth weight by 10.75 percent. Materno-fetal mitochondrial and apoptotic PBMC and CBMC parameters showed altered and correlated values regarding COX activity, mitochondrial DNA, oxidative stress and apoptosis. Placenta partially compensated this dysfunction by increasing mitochondrial number; even so ratios of oxidative stress and apoptosis were increased. A CO-induced mitotoxic and apoptotic fingerprint is present in smoking pregnant women and their newborn, with a lack of filtering effect from the placenta. Tobacco consumption correlated with a reduction in birth weight and mitochondrial and apoptotic impairment, suggesting that both could be the cause of the reduced birth weight in smoking pregnant women.

Carbon monoxide modulates cytochrome oxidase activity and oxidative stress in the developing murine brain during isoflurane exposure

Commonly used anesthetics induce widespread neuronal degeneration in the developing mammalian brain via the oxidative-stress-associated mitochondrial apoptosis pathway. Dysregulation of cytochrome oxidase (CcOX), the terminal oxidase of the electron transport chain, can result in reactive oxygen species (ROS) formation. Isoflurane has previously been shown to activate this enzyme. Carbon monoxide (CO), as a modulator of CcOX, is of interest because infants and children are routinely exposed to CO during low-flow anesthesia. We have recently demonstrated that low concentrations of CO limit and prevent isoflurane-induced neurotoxicity in the forebrains of newborn mice in a dose-dependent manner. However, the effect of CO on CcOX in the context of anesthetic-induced oxidative stress is unknown. Seven-day-old male CD-1 mice underwent 1h exposure to 0 (air), 5, or 100ppm CO in air with or without isoflurane. Exposure to isoflurane or CO independently increased CcOX kinetic activity and increased ROS within forebrain mitochondria. However, exposure to CO combined with isoflurane paradoxically limited CcOX activation and oxidative stress. There were no changes seen in steady-state levels of CcOX I protein, indicating post-translational modification of CcOX as an etiology for changes in enzyme activity. CO exposure led to differential effects on CcOX subunit I tyrosine phosphorylation depending on concentration, while combined exposure to isoflurane with CO markedly increased the enzyme phosphorylation state. Phosphorylation of tyrosine 304 of CcOX subunit I has been shown to result in strong enzyme inhibition, and the relative reduction in CcOX kinetics following exposure to CO combined with isoflurane may have been due, in part, to such phosphorylation. Taken together, the data suggest that CO modulates CcOX in the developing brain during isoflurane exposure, thereby limiting oxidative stress. These CO-mediated effects could have implications for the development of low-flow anesthesia in infants and children to prevent anesthesia-induced oxidative stress.

Carbon monoxide released by CORM-401 uncouples mitochondrial respiration and inhibits glycolysis in endothelial cells: A role for mitoBKCa channels

Carbon monoxide (CO), a product of heme degradation by heme oxygenases, plays an important role in vascular homeostasis. Recent evidence indicates that mitochondria are among a number of molecular targets that mediate the cellular actions of CO. In the present study we characterized the effects of CO released from CORM-401 on mitochondrial respiration and glycolysis in intact human endothelial cells using electron paramagnetic resonance (EPR) oximetry and the Seahorse XF technology. We found that CORM-401 (10-100μM) induced a persistent increase in the oxygen consumption rate (OCR) that was accompanied by inhibition of glycolysis (extracellular acidification rate, ECAR) and a decrease in ATP-turnover. Furthermore, CORM-401 increased proton leak, diminished mitochondrial reserve capacity and enhanced non-mitochondrial respiration. Inactive CORM-401 (iCORM-401) neither induced mitochondrial uncoupling nor inhibited glycolysis, supporting a direct role of CO in the endothelial metabolic response induced by CORM-401. Interestingly, blockade of mitochondrial large-conductance calcium-regulated potassium ion channels (mitoBKCa) with paxilline abolished the increase in OCR promoted by CORM-401 without affecting ECAR; patch-clamp experiments confirmed that CO derived from CORM-401 activated mitoBKCa channels present in mitochondria. Conversely, stabilization of glycolysis by MG132 prevented CORM-401-mediated decrease in ECAR but did not modify the OCR response. In summary, we demonstrated in intact endothelial cells that CO induces a two-component metabolic response: uncoupling of mitochondrial respiration dependent on the activation of mitoBKCa channels and inhibition of glycolysis independent of mitoBKCa channels.

Confocal and fluorescence lifetime imaging sheds light on the fate of a pyrene-tagged carbon monoxide-releasing Fischer carbene chromium complex

The synthesis of a new pyrene-containing Fischer carbene complex is described. The complex has a broad absorbance spectrum between 300 and 400 nm and, on excitation at 345 nm in CH2Cl2 solution, emission is observed at 395 and 415 nm. Emission is also observed in PBS buffer, but in this case the resulting spectra are much broader. Confocal and fluorescence lifetime imaging indicate that emission occurs on treating HeLa cells with the complex and co-localisation studies demonstrate that this is from the mitochondria and lipid-rich regions of the cell.

Carbon monoxide and the CNS: challenges and achievements

Haem oxygenase (HO) and its product carbon monoxide (CO) are associated with cytoprotection and maintenance of homeostasis in several different organs and tissues. This review focuses upon the role of exogenous and endogenous CO (via HO activity and expression) in various CNS pathologies, based upon data from experimental models, as well as from some clinical data on human patients. The pathophysiological conditions reviewed are cerebral ischaemia, chronic neurodegenerative diseases (Alzheimer's and Parkinson's diseases), multiple sclerosis and pain. Among these pathophysiological conditions, a variety of cellular mechanisms and processes are considered, namely cytoprotection, cell death, inflammation, cell metabolism, cellular redox responses and vasomodulation, as well as the different targeted neural cells. Finally, novel potential methods and strategies for delivering exogenous CO as a drug are discussed, particularly approaches based upon CO-releasing molecules, their limitations and challenges. The diagnostic and prognostic value of HO expression in clinical use for brain pathologies is also addressed.

Carbon monoxide and mitochondria-modulation of cell metabolism, redox response and cell death

Carbon monoxide (CO) is an endogenously produced gasotransmitter, which is associated with cytoprotection and cellular homeostasis in several distinct cell types and tissues. CO mainly targets mitochondria because: (i) mitochondrial heme-proteins are the main potential candidates for CO to bind, (ii) many CO's biological actions are dependent on mitochondrial ROS signaling and (iii) heme is generated in the mitochondrial compartment. Mitochondria are the key cell energy factory, producing ATP through oxidative phosphorylation and regulating cell metabolism. These organelles are also implicated in many cell signaling pathways and the production of reactive oxygen species (ROS). Finally, mitochondria contain several factors activating programmed cell death pathways, which are released from the mitochondrial inter-membrane space upon mitochondrial membrane permeabilization. Therefore, disclosing CO mode of action at mitochondria opens avenues for deeper understanding CO's biological properties. Herein, it is discussed how CO affects the three main aspects of mitochondrial modulation of cell function: metabolism, redox response and cell death.

Carbon Monoxide-Releasing Molecules Attenuate Postresuscitation Myocardial Injury and Protect Cardiac Mitochondrial Function by Reducing the Production of Mitochondrial Reactive Oxygen Species in a Rat Model of Cardiac Arrest

The objective of this study is to examine whether carbon monoxide-releasing molecules (CORMs) can decrease the generation of excessive reactive oxygen species (ROS) in cardiac mitochondria, thereby protecting against postresuscitation myocardial injury and cardiac mitochondrial dysfunction after resuscitation in a rat model of ventricular fibrillation (VF), and further investigated the underlying mechanism. Rats suffered 8 minutes of untreated VF and resuscitation and were randomized into the control group with vehicle infusion and the CORM group with CO-releasing molecule 2 (CORM2) treatment. Animals in the Sham group were instrumented without induced VF and resuscitation. Effects of CORM2 on cardiac function, myocardial oxidative stress, cardiac mitochondrial function, and mitochondrial ROS generation were assessed. Moreover, to further evaluate the direct effect of CORM2 on cardiac mitochondria isolated from resuscitated rats, we measured mitochondrial function and ROS generation when isolated cardiac mitochondria were directly incubated with different concentrations of (CORM2). Compared with the Sham group, the control and CORM groups demonstrated impaired cardiac function, increased myocardial injury, and aggravated mitochondrial damage. CORM2 improved cardiac performance and attenuated myocardial damage and oxidative stress in resuscitated rats. Additionally, animals with CORM2 treatment showed the decreased generation of cardiac mitochondrial ROS, alleviated mitochondrial injury, and preserved mitochondrial function and complex activities when compared with the control group. In isolated cardiac mitochondria incubated with CORM2, low concentrations of CORM2 (20 μmol/L) mildly uncoupled mitochondrial respiration, leading to reduced mitochondrial ROS production. In contrast, high concentrations of CORM2 (60 μmol/L) resulted in the reverse effect presumably due to its excessive uncoupling action. These findings suggest that CORM2 attenuates oxidative stress of the heart and improves cardiac function after resuscitation. The mechanism was probably that CO, the product of CORM2, reduces the production of cardiac mitochondrial ROS and thereby attenuates mitochondrial injury and dysfunction during the postresuscitation period, due to the transient uncoupling of mitochondrial respiration.

Mitochondrial toxicity in human pregnancy: an update on clinical and experimental approaches in the last 10 years

Mitochondrial toxicity can be one of the most dreadful consequences of exposure to a wide range of external agents including pathogens, therapeutic agents, abuse drugs, toxic gases and other harmful chemical substances. However, little is known about the effects of mitochondrial toxicity on pregnant women exposed to these agents that may exert transplacental activity and condition fetal remodeling. It has been hypothesized that mitochondrial toxicity may be involved in some adverse obstetric outcomes. In the present study, we investigated the association between exposure to mitochondrial toxic agents and pathologic conditions ranging from fertility defects, detrimental fetal development and impaired newborn health due to intra-uterine exposure. We have reviewed data from studies in human subjects to propose mechanisms of mitochondrial toxicity that could be associated with the symptoms present in both exposed pregnant and fetal patients. Since some therapeutic interventions or accidental exposure cannot be avoided, further research is needed to gain insight into the molecular pathways leading to mitochondrial toxicity during pregnancy. The ultimate objective of these studies should be to reduce the mitochondrial toxicity of these agents and establish biomarkers for gestational monitoring of harmful effects.

Patent Highlights

A snapshot of noteworthy recent developments in the patent literature of relevance to pharmaceutical and medical research and development.

Heme oxygenase-1: a metabolic nike

SIGNIFICANCE

Heme degradation, which was described more than 30 years ago, is still very actively explored with many novel discoveries on its role in various disease models every year.

RECENT ADVANCES

The heme oxygenases (HO) are metabolic enzymes that utilize NADPH and oxygen to break apart the heme moiety liberating biliverdin (BV), carbon monoxide (CO), and iron. Heme that is derived from hemoproteins can be toxic to the cells and if not removed immediately, it causes cell apoptosis and local inflammation. Elimination of heme from the milieu enables generation of three products that influences numerous metabolic changes in the cell.

CRITICAL ISSUES

CO has profound effects on mitochondria and cellular respiration and other hemoproteins to which it can bind and affect their function, while BV and bilirubin (BR), the substrate and product of BV, reductase, respectively, are potent antioxidants. Sequestration of iron into ferritin and its recycling in the tissues is a part of the homeodynamic processes that control oxidation-reduction in cellular metabolism. Further, heme is an important component of a number of metabolic enzymes, and, therefore, HO-1 plays an important role in the modulation of cellular bioenergetics.

FUTURE DIRECTIONS

In this review, we describe the cross-talk between heme oxygenase-1 (HO-1) and its products with other metabolic pathways. HO-1, which we have labeled Nike, the goddess who personified victory, dictates triumph over pathophysiologic conditions, including diabetes, ischemia, and cancer.

Carbon monoxide releasing molecule‑2 attenuated ischemia/reperfusion‑induced apoptosis in cardiomyocytes via a mitochondrial pathway

Carbon monoxide (CO) is an endogenous gaseous transmitter that exerts multi-protection in ischemia/reperfusion (I/R) injury, but few experimental studies regarding CO on myocardial I/R-induced apoptosis, as well as its underlying mechanism have been conducted. The present study was designed to investigate whether CO released from CO-releasing molecule-2 (CORM-2) is capable of ameliorating myocardial I/R-induced apoptosis via a mitochondrial apoptotic pathway. Primary cultures of neonatal rat cardiomyocytes were randomly distributed into four groups: Control, I/R (cultured cardiomyocytes were subjected to 2 h simulated ischemia followed by 4 h reperfusion), CORM-2 and inactive CORM-2 (iCORM-2) groups (20 µM CORM-2 and 20 µM iCORM-2 were administered at the beginning of reperfusion following ischemia, respectively). Flow cytometric analysis showed that CORM-2 treatment significantly decreased apoptosis of cardiomyocytes triggered by simulated I/R. CORM-2 partially recovered mitochondrial respiration and ultrastructure alteration, and lowered caspase-3 expression and the release of cytochrome c. Furthermore, CORM-2 partly reduced BAK/BAX expression in mitochondria, as well as the BAX level in the cytoplasm. Cardioprotection is lost when CORM-2 is replaced by iCORM-2. CORM-2 treatment, at the time of reperfusion, was concluded to attenuate myocardial I/R-induced apoptosis. The protection mechanisms may be targeted to the mitochondria and involved in the inhibition of the BAK/BAX‑mediated intrinsic pathway.