Pre-conditioning induced by carbon monoxide provides neuronal protection against apoptosis

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.

Gasotransmitters and noble gases in cardioprotection: unraveling molecular pathways for future therapeutic strategies

Despite recent progress, ischemic heart disease poses a persistent global challenge, driving significant morbidity and mortality. The pursuit of therapeutic solutions has led to the emergence of strategies such as ischemic preconditioning, postconditioning, and remote conditioning to shield the heart from myocardial ischemia/reperfusion injury (MIRI). These ischemic conditioning approaches, applied before, after, or at a distance from the affected organ, inspire future therapeutic strategies, including pharmacological conditioning. Gasotransmitters, comprising nitric oxide, hydrogen sulfide, sulfur dioxide, and carbon monoxide, play pivotal roles in physiological and pathological processes, exhibiting shared features such as smooth muscle relaxation, antiapoptotic effects, and anti-inflammatory properties. Despite potential risks at high concentrations, physiological levels of gasotransmitters induce vasorelaxation and promote cardioprotective effects. Noble gases, notably argon, helium, and xenon, exhibit organ-protective properties by reducing cell death, minimizing infarct size, and enhancing functional recovery in post-ischemic organs. The protective role of noble gases appears to hinge on their modulation of molecular pathways governing cell survival, leading to both pro- and antiapoptotic effects. Among noble gases, helium and xenon emerge as particularly promising in the field of cardioprotection. This overview synthesizes our current understanding of the roles played by gasotransmitters and noble gases in the context of MIRI and cardioprotection. In addition, we underscore potential future developments involving the utilization of noble gases and gasotransmitter donor molecules in advancing cardioprotective strategies.

Clearing the Smoke: What Protects Smokers from Parkinson's Disease?

The link between smoking and a lower risk of Parkinson's disease (PD) is one of the strongest environmental or lifestyle associations in neuroepidemiology. Growing evidence supports the hypothesis that the association is based on a neuroprotective effect of smoking on PD, despite the plausible alternative that smoking serves as a marker for a proximal protective influence without itself conferring benefit. But how smoking could protect against neurodegeneration in PD is not well understood. Of several candidate molecules and mechanisms that have been nominated, nicotine has received the most attention. However, randomized controlled clinical trials of nicotine in PD have failed to demonstrate benefit on motor endpoints, including the NIC-PD study in which recently diagnosed participants were randomly assigned to placebo or nicotine treatment for 1 year. Given these results, the time is right to evaluate the neuroprotective potential of other molecules and biochemical cascades triggered by smoking. Here, we review the evidence supporting smoking's possible protective effect on PD, compounds in tobacco and smoke that might mediate such benefit, and non-causal classes of explanation, including reverse causation and the prospect of shared genetic determinants of smoking and PD resistance. The therapeutic potential of non-nicotine components of smoke is suggested by studies supporting multiple alternative mechanisms ranging from monoamine oxidase inhibitors to gut microbiome disruption to antioxidant response induction by chronic exposure to low levels of carbon monoxide. Rigorous investigation is warranted to evaluate this molecule and others for disease-preventing and disease-modifying activity in PD models and, if warranted, in clinical trials. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Carboxyhemoglobin (COHb): Unavoidable Bystander or Protective Player?

Carbon monoxide (CO) is a cytoprotective endogenous gas that is ubiquitously produced by the stress response enzyme heme-oxygenase. Being a gas, CO rapidly diffuses through tissues and binds to hemoglobin (Hb) increasing carboxyhemoglobin (COHb) levels. COHb can be formed in erythrocytes or in plasma from cell-free Hb. Herein, it is discussed as to whether endogenous COHb is an innocuous and inevitable metabolic waste product or not, and it is hypothesized that COHb has a biological role. In the present review, literature data are presented to support this hypothesis based on two main premises: (i) there is no direct correlation between COHb levels and CO toxicity, and (ii) COHb seems to have a direct cytoprotective and antioxidant role in erythrocytes and in hemorrhagic models in vivo. Moreover, CO is also an antioxidant by generating COHb, which protects against the pro-oxidant damaging effects of cell-free Hb. Up to now, COHb has been considered as a sink for both exogenous and endogenous CO generated during CO intoxication or heme metabolism, respectively. Hallmarking COHb as an important molecule with a biological (and eventually beneficial) role is a turning point in CO biology research, namely in CO intoxication and CO cytoprotection.

Carbon monoxide preconditioning is mediated via activation of mitochondrial-derived vesicles

Preconditioning with inhalative carbon monoxide (CO) at low concentrations provides protection against hypoxic and ischemic insults in the brain and heart. The present study aims to test a hypothesis that activation of mitochondrial-derived vesicles (MDVs) is a mechanism underlying the protective effect of CO preconditioning. Here we show that CO preconditioning induced mild oxidative stress and activated massive production of MDVs. Short exposure to a low concentration of carbon monoxide-releasing molecule 2 (CORM-2), a donor of carbon monoxide, prevented oligodendrocyte precursor cells (OPCs) from subsequent death induced by high doses of CO, and protected Chinese hamster ovary (CHO) cells against oxygen-glucose deprivation (OGD)-induced cell death. Furthermore, inhibition of lysosomal activity prevented degradation of MDVs, abolished MDV-mediated mitochondrial quality control, and diminished the protective effect of CO preconditioning. Altogether, our data provide direct evidence suggesting that MDV-mediated mitochondrial quality control may have a novel role in CO preconditioning.

Carbon Monoxide Stimulates Both Mitophagy And Mitochondrial Biogenesis to Mediate Protection Against Oxidative Stress in Astrocytes

Astrocytes are key glial cells for the metabolic and functional support of the brain. Mitochondrial quality control (MQC), in particular the balance between mitophagy and mitochondrial biogenesis, is a major event for the maintenance of cellular homeostasis. Carbon monoxide (CO) is an endogenous gasotransmitter that inhibits cell death and inflammation by targeting mitochondria. It is well established that CO promotes cytoprotection by increasing mitochondrial population and metabolism (oxidative phosphorylation). Thus, it is hypothesized that CO-induced cytoprotection may also be mediated by the balance between mitophagy and mitochondrial biogenesis. Herein, the carbon monoxide releasing molecule-A1 (CORM-A1) was used in primary cultures of astrocytes to assess CO role on mitochondrial turnover. PINK1/Parkin-dependent mitophagy was stimulated by CORM-A1 following 1 h of treatment. While at 24 h after treatment, CORM-A1 increased mitochondrial population, which may indicate mitochondrial biogenesis. In fact, mitochondrial biogenesis was confirmed by the enhancement of PGC-1α expression that upregulates several mitochondrial transcription factors. Furthermore, inhibition of mitophagy by knocking down PINK1 expression reverted CO-induced mitochondrial biogenesis, indicating that mitochondrial turnover is dependent on modulation of mitophagy. Finally, CORM-A1 prevented astrocytic cell death induced by oxidative stress in a mitophagy-dependent manner. In fact, whenever PINK1 was knocked down, CORM-A1-induced cytoprotection was lost. In summary, CORM-A1 stimulates mitochondrial turnover, which in turn prevents astrocytic cell death. CO cytoprotection depends on increasing mitochondrial population and on eliminating dysfunctional mitochondria.

Medical Gas Therapy for Tissue, Organ, and CNS Protection: A Systematic Review of Effects, Mechanisms, and Challenges

Gaseous molecules have been increasingly explored for therapeutic development. Here, following an analytical background introduction, a systematic review of medical gas research is presented, focusing on tissue protections, mechanisms, data tangibility, and translational challenges. The pharmacological efficacies of carbon monoxide (CO) and xenon (Xe) are further examined with emphasis on intracellular messengers associated with cytoprotection and functional improvement for the CNS, heart, retina, liver, kidneys, lungs, etc. Overall, the outcome supports the hypothesis that readily deliverable "biological gas" (CO, H2 , H2 S, NO, O2 , O3 , and N2 O) or "noble gas" (He, Ar, and Xe) treatment may preserve cells against common pathologies by regulating oxidative, inflammatory, apoptotic, survival, and/or repair processes. Specifically, CO, in safe dosages, elicits neurorestoration via igniting sGC/cGMP/MAPK signaling and crosstalk between HO-CO, HIF-1α/VEGF, and NOS pathways. Xe rescues neurons through NMDA antagonism and PI3K/Akt/HIF-1α/ERK activation. Primary findings also reveal that the need to utilize cutting-edge molecular and genetic tactics to validate mechanistic targets and optimize outcome consistency remains urgent; the number of neurotherapeutic investigations is limited, without published results from large in vivo models. Lastly, the broad-spectrum, concurrent multimodal homeostatic actions of medical gases may represent a novel pharmaceutical approach to treating critical organ failure and neurotrauma.

The brain heme oxygenase/biliverdin reductase system as a target in drug research and development

INTRODUCTION

The heme oxygenase/biliverdin reductase (HO/BVR) system is involved in heme metabolism. The inducible isoform of HO (HO-1) and BVR both exert cytoprotective effects by enhancing cell stress response. In this context, some xenobiotics, which target HO-1, including herbal products, behave as neuroprotectants in several experimental models of neurodegeneration. Despite this, no drug having either HO-1 or BVR as a main target is currently available.

AREAS COVERED

After a description of the brain HO/BVR system, the paper analyzes the main classes of drugs acting on the nervous system, with HO as second-level target, and their neuroprotective potential. Finally, the difficulties that exist for the development of drugs acting on HO/BVR and the possible ways to overcome these hurdles are examined.

EXPERT OPINION

Although the limited clinical evidence has restricted the translational research on the HO/BVR system, mainly because of the dual nature of its by-products, there has been growing interest in the therapeutic potential of these enzymes. Scientists should boost the translational research on the HO/BVR system which could be supported by the significant evidence provided by preclinical studies.

Demethylation of Artificial Hydrogenase Agent for Prolonged CO Release and Enhanced Anti-Tau Aggregation Activity

Carbon Monoxide (CO) plays an important role in signaling in the cells, making its use as a therapeutic tool highly intriguing. Reduced burst emissions are important to avoid the cytotoxicity...

Carbon Monoxide-Neuroglobin Axis Targeting Metabolism Against Inflammation in BV-2 Microglial Cells

Microglia are the immune competent cell of the central nervous system (CNS), promoting brain homeostasis and regulating inflammatory response against infection and injury. Chronic or exacerbated neuroinflammation is a cause of damage in several brain pathologies. Endogenous carbon monoxide (CO), produced from the degradation of heme, is described as anti-apoptotic and anti-inflammatory in several contexts, including in the CNS. Neuroglobin (Ngb) is a haemoglobin-homologous protein, which upregulation triggers antioxidant defence and prevents neuronal apoptosis. Thus, we hypothesised a crosstalk between CO and Ngb, in particular, that the anti-neuroinflammatory role of CO in microglia depends on Ngb. A novel CO-releasing molecule (ALF826) based on molybdenum was used for delivering CO in microglial culture.BV-2 mouse microglial cell line was challenged with lipopolysaccharide (LPS) for triggering inflammation, and after 6 h ALF826 was added. CO exposure limited inflammation by decreasing inducible nitric oxide synthase (iNOS) expression and the production of nitric oxide (NO) and tumour necrosis factor-α (TNF-α), and by increasing interleukine-10 (IL-10) release. CO-induced Ngb upregulation correlated in time with CO's anti-inflammatory effect. Moreover, knocking down Ngb reversed the anti-inflammatory effect of CO, suggesting that dependents on Ngb expression. CO-induced Ngb upregulation was independent on ROS signalling, but partially dependent on the transcriptional factor SP1. Finally, microglial cell metabolism is also involved in the inflammatory response. In fact, LPS treatment decreased oxygen consumption in microglia, indicating a switch to glycolysis, which is associated with a proinflammatory. While CO treatment increased oxygen consumption, reverting LPS effect and indicating a metabolic shift into a more oxidative metabolism. Moreover, in the absence of Ngb, this phenotype was no longer observed, indicating Ngb is needed for CO's modulation of microglial metabolism. Finally, the metabolic shift induced by CO did not depend on alteration of mitochondrial population. In conclusion, neuroglobin emerges for the first time as a key player for CO signalling against exacerbated inflammation in microglia.

Carbon Monoxide Modulation of Microglia-Neuron Communication: Anti-Neuroinflammatory and Neurotrophic Role

Microglia, the 'resident immunocompetent cells' of the central nervous system (CNS), are key players in innate immunity, synaptic refinement and homeostasis. Dysfunctional microglia contribute heavily to creating a toxic inflammatory milieu, a driving factor in the pathophysiology of several CNS disorders. Therefore, strategies to modulate the microglial function are required to tackle exacerbated tissue inflammation. Carbon monoxide (CO), an endogenous gaseous molecule produced by the degradation of haem, has anti-inflammatory, anti-apoptotic, and pro-homeostatic and cytoprotective roles, among others. ALF-826A, a novel molybdenum-based CO-releasing molecule, was used for the assessment of neuron-microglia remote communication. Primary cultures of rat microglia and neurons, or the BV-2 microglial and CAD neuronal murine cell lines, were used to study the microglia-neuron interaction. An approach based on microglial-derived conditioned media in neuronal culture was applied. Medium derived from CO-treated microglia provided indirect neuroprotection against inflammation by limiting the lipopolysaccharide (LPS)-induced expression of reactivity markers (CD11b), the production of reactive oxygen species (ROS) and the secretion of inflammatory factors (TNF-α, nitrites). This consequently prevented neuronal cell death and maintained neuronal morphology. In contrast, in the absence of inflammatory stimulus, conditioned media from CO-treated microglia improved neuronal morphological complexity, which is an indirect manner of assessing neuronal function. Likewise, the microglial medium also prevented neuronal cell death induced by pro-oxidant tert-Butyl hydroperoxide (t-BHP). ALF-826 treatment reinforced microglia secretion of Interleukin-10 (IL-10) and adenosine, mediators that may protect against t-BHP stress in this remote communication model. Chemical inhibition of the adenosine receptors A_2A and A₁ reverted the CO-derived neuroprotective effect, further highlighting a role for CO in regulating neuron-microglia communication via purinergic signalling. Our findings indicate that CO has a modulatory role on microglia-to-neuron communication, promoting neuroprotection in a non-cell autonomous manner. CO enhances the microglial release of neurotrophic factors and blocks exacerbated microglial inflammation. CO improvement of microglial neurotrophism under non-inflammatory conditions is here described for the first time.

Potential therapeutic effects of Nrf2 activators on intracranial hemorrhage

Intracranial hemorrhage (ICH) is a devastating disease which induces high mortality and poor outcomes including severe neurological dysfunctions. ICH pathology is divided into two types: primary brain injury (PBI) and secondary brain injury (SBI). Although there are numerous preclinical studies documenting neuroprotective agents in experimental ICH models, no effective drugs have been developed for clinical use due to complicated ICH pathology. Oxidative and inflammatory stresses play central roles in the onset and progression of brain injury after ICH, especially SBI. Nrf2 is a crucial transcription factor in the anti-oxidative stress defense system. Under normal conditions, Nrf2 is tightly regulated by the Keap1. Under ICH pathological conditions, such as overproduction of reactive oxygen species (ROS), Nrf2 is translocated into the nucleus where it up-regulates the expression of several anti-oxidative phase II enzymes such as heme oxygenase-1 (HO-1). Recently, many reports have suggested the therapeutic potential of Nrf2 activators (including natural or synthesized compounds) for treating neurodegenerative diseases. Moreover, several Nrf2 activators attenuate ischemic stroke-induced brain injury in several animal models. This review summarizes the efficacy of several Nrf2 activators in ICH animal models. In the future, Nrf2 activators might be approved for the treatment of ICH patients.

Administration of inhaled noble and other gases after cardiopulmonary resuscitation: A systematic review

OBJECTIVE

Inhalation of noble and other gases after cardiac arrest (CA) might improve neurological and cardiac outcomes. This article discusses up-to-date information on this novel therapeutic intervention.

DATA SOURCES

CENTRAL, MEDLINE, online published abstracts from conference proceedings, clinical trial registry clinicaltrials.gov, and reference lists of relevant papers were systematically searched from January 1960 till March 2019.

STUDY SELECTION

Preclinical and clinical studies, irrespective of their types or described outcomes, were included.

DATA EXTRACTION

Abstract screening, study selection, and data extraction were performed by two independent authors. Due to the paucity of human trials, risk of bias assessment was not performed DATA SYNTHESIS: After screening 281 interventional studies, we included an overall of 27. Only, xenon, helium, hydrogen, and nitric oxide have been or are being studied on humans. Xenon, nitric oxide, and hydrogen show both neuroprotective and cardiotonic features, while argon and hydrogen sulfide seem neuroprotective, but not cardiotonic. Most gases have elicited neurohistological protection in preclinical studies; however, only hydrogen and hydrogen sulfide appeared to preserve CA1 sector of hippocampus, the most vulnerable area in the brain for hypoxia.

CONCLUSION

Inhalation of certain gases after CPR appears promising in mitigating neurological and cardiac damage and may become the next successful neuroprotective and cardiotonic interventions.

CORM-3 ameliorates neurodegeneration in the amygdala and improves depression- and anxiety-like behavior in a rat model of combined traumatic brain injury and hemorrhagic shock

OBJECTIVE

Emotional disturbances characterized by depression and anxiety among survivors of traumatic brain injury (TBI) impact the quality of life severely. Currently, there is a lack of effective drug treatment for neurodegeneration induced by TBI, mainly due to failed efficacy of compounds such as corticosteroids, calcium channel blockers, and excitatory amino acid inhibitors. Thus, we sought to continue with our investigation on CORM-3, a water-soluble exogenous carbon monoxide-releasing molecule with excellent anti-inflammatory actions employed in a previous study using a rat model of combined TBI with hemorrhage shock and resuscitation (HSR).

METHODS

Rats were administrated with CORM-3 after induction of TBI and HSR and examined depressive and anxiety-like behaviors, along with cerebral function employing functional magnetic resonance imaging (MRI) 30-days post-trauma. Also, the following variables were measured: 1) neuronal pyroptosis and apoptosis 24 h post-trauma, 2) the roles of PKG-ERK1/2 signaling pathways with the use of the protein kinase G (PKG) specific inhibitor, KT5823.

RESULTS

CORM-3-treated rats displayed significant ameliorated depression- and anxiety-like behaviors, improved cerebral blood flow, and fractional anisotropy (FA), showed less neuronal pyroptosis and apoptosis in the amygdala, and upregulated the phosphorylation of Vasodilator-stimulated phosphoprotein (VASP) and ERK1/2. However, CORM-3 neuroprotective effects against trauma were only partially reversed by KT5823.

CONCLUSION

CORM-3 ameliorated the emotional deficits and neuronal death induced in the amygdala post-TBI and HSR rat model, and PKG-ERK1/2 signaling might be implicated in the underlying mechanism.

Carbon monoxide controls microglial erythrophagocytosis by regulating CD36 surface expression to reduce the severity of hemorrhagic injury

Microglial erythrophagocytosis is crucial in injury response to hemorrhagic stroke. We hypothesized that regulation of microglial erythrophagocytosis via HO-1/CO depends on a pathway involving reactive oxygen species (ROS) and CD36 surface-expression. The microglial BV-2 cell line and primary microglia (PMG) were incubated +/-blood and +/-CO-exposure. PMG isolated from tissue-specific HO-1-deficient (LyzM-Cre-Hmox1 ^fl/fl ) and CD36 ^-/- mice or siRNA against AMPK (AMP-activated protein kinase) were used to test our hypothesis. In a murine subarachnoid hemorrhage (SAH) model, we compared neuronal injury in wild-type and CD36 ^-/- mice. Readouts included vasospasm, microglia activation, neuronal apoptosis, and spatial memory. We observed increased microglial HO-1-expression after blood-exposure. A burst in ROS-production was seen after CO-exposure, which led to increased amounts of phosphorylated AMPK with subsequently enhanced CD36 surface-expression. Naïve PMG from LyzM-Cre-Hmox1 ^fl/fl mice showed reduced ROS-production and CD36 surface-expression and failed to respond to CO with increased CD36 surface-expression. Lack of HO-1 and CD36 resulted in reduced erythrophagocytosis that could not be rescued with CO. Erythrophagocytosis was enhanced in BV-2 cells in the presence of exogenous CO, which was abolished in cells treated with siRNA to AMPK. CD36 ^-/- mice subjected to SAH showed enhanced neuronal cell death, which resulted in impaired spatial memory function. We demonstrate that microglial phagocytic function partly depends on a pathway involving HO-1 with changes in ROS-production, phosphorylated AMPK, and surface expression of CD36. CD36 was identified as a crucial component in blood clearance after hemorrhage that ultimately determines neuronal outcome. These results demand further investigations studying the potential neuroprotective properties of CO.

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.

The development of a hemicyanine-based ratiometric CO fluorescent probe with a long emission wavelength and its applications for imaging COin vitroandin vivo

A novel ratiometric fluorescent probe,Hcy-CO, with long-wavelength emission was developed for visualizing CO in living cells and zebrafish.

Investigating in Vitro Amyloid Peptide 1-42 Aggregation: Impact of Higher Molecular Weight Stable Adducts

The self-assembly of amyloid peptides (Aβ), in particular Aβ_1-42, into oligomers and fibrils is one of the main pathological events related to Alzheimer's disease. Recent studies have demonstrated the ability of carbon monoxide-releasing molecules (CORMs) to protect neurons and astrocytes from Aβ_1-42 toxicity. In fact, CORMs are able to carry and release controlled levels of CO and are known to exert a wide range of anti-inflammatory and anti-apoptotic activities at physiologically relevant concentrations. In order to investigate the direct effects of CORMs on Aβ_1-42, we studied the reactivity of CORM-2 and CORM-3 with Aβ_1-42 in vitro and the potential inhibition of its aggregation by mass spectrometry (MS), as well as fluorescence and circular dichroism spectroscopies. The application of an electrospray ionization-MS (ESI-MS) method allowed the detection of stable Aβ_1-42/CORMs adducts, involving the addition of the Ru(CO)₂ portion of CORMs at histidine residues on the Aβ_1-42 skeleton. Moreover, CORMs showed anti-aggregating properties through formation of stable adducts with Aβ_1-42 as demonstrated by a thioflavin T fluorescence assay and MS analysis. As further proof, comparison of the CD spectra of Aβ_1-42 recorded in the absence and in the presence of CORM-3 at a 1:1 molar ratio showed the ability of CORM-3 to stabilize the peptide in its soluble, unordered conformation, thereby preventing its misfolding and aggregation. This multi-methodological investigation revealed novel interactions between Aβ_1-42 and CORMs, contributing new insights into the proposed neuroprotective mechanisms mediated by CORMs and disclosing a new strategy to divert amyloid aggregation and toxicity.

Carbon monoxide released by CORM-A1 prevents yeast cell death via autophagy stimulation

Autophagy is an autodigestive process, promoting cytoprotection by the elimination of dysfunctional organelles, misfolded proteins and toxic aggregates. Carbon monoxide (CO) is an endogenous gasotransmitter that under low concentrations prevents cell death and inflammation. For the first time, the role of autophagy in CO-mediated cytoprotection against oxidative stress was evaluated in the model yeast Saccharomyces cerevisiae. The boron-based CO-releasing molecule, CORM-A1, was used to deliver CO. CORM-A1 partially prevented oxidative stress-induced cell death in yeast. Likewise, CORM-A1 activated autophagy under basal physiological conditions, which were assessed by autophagic flux and the expression of mCherry-Atg8 or GFP-Atg8. Inhibition of autophagy by knocking out key autophagic genes in yeast (ATG8 or ATG11) blocked CORM-A1 cytoprotective effect, indicating the critical role of autophagy in CO-induced cytoprotection. The CO-mediated cytoprotection via autophagy induction observed in yeast was validated in primary cultures of astrocytes, a well-characterized model for CO's cytoprotective functions. As in yeast, CORM-A1 prevented oxidative stress-induced cell death in an autophagy-dependent manner in astrocytes. Overall, our data support the cytoprotective action of CO against oxidative stress. CO promotes cytoprotection in yeast via autophagy, opening new possibilities for the study of molecular mechanisms of CO's biological functions using this powerful eukaryotic model.

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.

Heme oxygenase-1 as a potential therapeutic target in rheumatic diseases

BACKGROUND

Heme oxygenase-1 (HO-1), a cellular stress protein, serves a vital metabolic function as the rate-limiting enzyme in the degradation of heme to generate carbon monoxide (CO), iron, and biliverdin (BR). HO-1 may function as one of the most momentous factors of cell adaptation to oxidase stress, as well as a regulator of inflammatory signaling programs through the generation of its biologically active end products. Intensive investigation is now focusing on the potential function of HO-1 in inflammatory disorders, among which rheumatic diseases are one of the principal issues.

METHODS

"Heme oxygenase-1", "rheumatic diseases"; "lupus", "rheumatic arthritis", "osteoarthritis" and "oxidative stress" were used as key words for searching in Pubmed and Google scholar database.

RESULTS

Collected information from the related articles revealed the important role of pathogenesis and therapeutic potential of HO-1 in rheumatic diseases. Conclusions and discussions HO-1 has potential as a target for the treatment of rheumatic diseases due to its characteristic anti-inflammatory and anti-oxidative role. However, it is essential to monitor the HO-1 expression during particular stage of the disorders, and levels of HO-1 in different tissues and organs should be further confirmed in order to correlate it with clinical symptoms and other hallmarks of rheumatic diseases.

Heme oxygenase 1 regulates apoptosis induced by heat stress in bovine ovarian granulosa cells via the ERK1/2 pathway

Heat stress can inhibit follicular development in dairy cows, and thus can affect their reproductive performance. Follicular granulosa cells can synthesize estrogen, that affects the development and differentiation of follicles by apoptosis. Heme oxygenase 1 (HO-1/heat shock protein 32) plays an antiapoptotic and cytoprotective role in various cells during stress-induced apoptosis, but little is known about its definitive function in bovine (ovarian) granulosa cells (bGCs). In our study, the roles and mechanism of HO-1 on the heat stress-induced apoptosis of bGCs were studied. Our results show that the expression of HO-1 was significantly increased under heat stress. Moreover, HO-1 silencing increased apoptosis, whereas its overexpression dampened apoptosis by regulating the expression of Bax/Bcl-2 and the levels of cleaved caspase-3. In addition, HO-1 can also play a cytoprotective role by affecting estrogen levels and decomposing heme to produce biologically active metabolite carbon monoxide (CO). Meanwhile, CO significantly increased the level of HO-1, decreased Bax/Bcl-2 levels, and inhibited the activation of extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathway. The apoptosis of ovarian GCs can affect the secretion of estrogen and lead to disorder of the ovarian microenvironment, thus affecting the normal function of the ovary. Our results indicate that HO-1 acts as a cytoprotective enzyme and plays a protective role in heat-induced apoptosis of bGCs. In conclusion, HO-1 and its metabolite CO inhibit the apoptosis of bGCs induced by heat stress through the ERK1/2 pathway. The results of this study provide a valuable clue for improving the fertility of heat stressed cows in summer.

The Role of Gaseous Molecules in Traumatic Brain Injury: An Updated Review

Traumatic brain injury (TBI) affects millions of people in China each year. TBI has a high mortality and often times a serious prognosis. The causative mechanisms of TBI during development and recovery from an injury remain vague, leaving challenges for the medical community to provide treatment options that improve prognosis and provide an optimal recovery. Biological gaseous molecules including nitric oxide (NO), carbon monoxide (CO), hydrogen sulfide (H₂S), and molecular hydrogen (H₂) have been found to play critical roles in physiological and pathological conditions in mammals. Accumulating evidence has found that these gaseous molecules can execute neuroprotection in many central nervous system (CNS) conditions due to their highly permeable properties allowing them to enter the brain. Considering the complicated mechanisms and the serious prognosis of TBI, effective and adequate therapeutic approaches are urgently needed. These four gaseous molecules can be potential attractive therapeutic intervention on TBI. In this review, we will present a comprehensive overview on the role of these four biological gasses in the development of TBI and their potential therapeutic applications.

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.

A Pilot Study of Inhaled CO Therapy in Neonatal Hypoxia-Ischemia: Carboxyhemoglobin Concentrations and Brain Volumes

Objective: The objective of this pilot study was to start evaluating the efficacy and the safety (i.e., carboxyhemoglobin concentration of carbon monoxide (CO)) as a putative neuroprotective therapy in neonates. Study Design: Neonatal C57BL/6 mice were exposed to CO at a concentration of either 200 or 250 ppm for a period of 1 h. The pups were then sacrificed at 0, 10, 20, 60, 120, 180, and 240 min after exposure to either concentration of CO, and blood was collected for analysis of carboxyhemoglobin. Following the safety study, 7-day-old pups underwent a unilateral carotid ligation. After recovery, the pups were exposed to a humidified gas mixture of 8% oxygen and 92% nitrogen for 20 min in a hypoxia chamber. One hour after the hypoxia exposure, the pups were randomized to one of two groups: air (HI+A) or carbon monoxide (HI+CO). An inhaled dose of 250 ppm of CO was administered to the pups for 1 h per day for a period of 3 days. At 7 days post-injury, the pups were sacrificed and the brains analyzed for cortical and hippocampal volumes. Results: CO exposure at 200 and 250 ppm produced a peak carboxyhemoglobin concentration of 21.52 ± 1.18% and 27.55 ± 3.58%, respectively. The carboxyhemoglobin concentrations decreased rapidly, reaching control concentrations by 60 min post exposure. At 14 days of age (7 days post injury), the HI+CO (treated with 1 h per day of 250 ppm of CO for 3 days post injury) had significant preservation of the ratio of ipsilateral to contralateral cortex (median 1.07, 25% 0.97, 75% 1.23, n = 10) compared the HI+A group (p < 0.05). Conclusion: CO exposure of 250 ppm did not reach carboxyhemoglobin concentrations which would induce acute neurologic abnormalities and was effective in preserving cortical volumes following hypoxic-ischemic injury.

Blood-brain barrier transport and neuroprotective potential of blackberry-digested polyphenols: an in vitro study

PURPOSE

Epidemiological and intervention studies have attempted to link the health effects of a diet rich in fruits and vegetables with the consumption of polyphenols and their impact in neurodegenerative diseases. Studies have shown that polyphenols can cross the intestinal barrier and reach concentrations in the bloodstream able to exert effects in vivo. However, the effective uptake of polyphenols into the brain is still regarded with some reservations. Here we describe a combination of approaches to examine the putative transport of blackberry-digested polyphenols (BDP) across the blood-brain barrier (BBB) and ultimate evaluation of their neuroprotective effects.

METHODS

BDP was obtained by in vitro digestion of blackberry extract and BDP major aglycones (hBDP) were obtained by enzymatic hydrolysis. Chemical characterization and BBB transport of extracts were evaluated by LC-MSⁿ. BBB transport and cytoprotection of both extracts was assessed in HBMEC monolayers. Neuroprotective potential of BDP was assessed in NT2-derived 3D co-cultures of neurons and astrocytes and in primary mouse cerebellar granule cells. BDP-modulated genes were evaluated by microarray analysis.

RESULTS

Components from BDP and hBDP were shown to be transported across the BBB. Physiologically relevant concentrations of both extracts were cytoprotective at endothelial level and BDP was neuroprotective in primary neurons and in an advanced 3D cell model. The major canonical pathways involved in the neuroprotective effect of BDP were unveiled, including mTOR signaling and the unfolded protein response pathway. Genes such as ASNS and ATF5 emerged as novel BDP-modulated targets.

CONCLUSIONS

BBB transport of BDP and hBDP components reinforces the health benefits of a diet rich in polyphenols in neurodegenerative disorders. Our results suggest some novel pathways and genes that may be involved in the neuroprotective mechanism of the BDP polyphenol components.

Polyphenols journey through blood-brain barrier towards neuronal protection

Age-related complications such as neurodegenerative disorders are increasing and remain cureless. The possibility of altering the progression or the development of these multifactorial diseases through diet is an emerging and attractive approach with increasing experimental support. We examined the potential of known bioavailable phenolic sulfates, arising from colonic metabolism of berries, to influence hallmarks of neurodegenerative processes. In silico predictions and in vitro transport studies across blood-brain barrier (BBB) endothelial cells, at circulating concentrations, provided evidence for differential transport, likely related to chemical structure. Moreover, endothelial metabolism of these phenolic sulfates produced a plethora of novel chemical entities with further potential bioactivies. Pre-conditioning with phenolic sulfates improved cellular responses to oxidative, excitotoxicity and inflammatory injuries and this attenuation of neuroinflammation was achieved via modulation of NF-κB pathway. Our results support the hypothesis that these small molecules, derived from dietary (poly)phenols may cross the BBB, reach brain cells, modulate microglia-mediated inflammation and exert neuroprotective effects, with potential for alleviation of neurodegenerative diseases.

Anesthesia-Related Carbon Monoxide Exposure: Toxicity and Potential Therapy

Exposure to carbon monoxide (CO) during general anesthesia can result from volatile anesthetic degradation by carbon dioxide absorbents and rebreathing of endogenously produced CO. Although adherence to the Anesthesia Patient Safety Foundation guidelines reduces the risk of CO poisoning, patients may still experience subtoxic CO exposure during low-flow anesthesia. The consequences of such exposures are relatively unknown. In contrast to the widely recognized toxicity of high CO concentrations, the biologic activity of low concentration CO has recently been shown to be cytoprotective. As such, low-dose CO is being explored as a novel treatment for a variety of different diseases. Here, we review the concept of anesthesia-related CO exposure, identify the sources of production, detail the mechanisms of overt CO toxicity, highlight the cellular effects of low-dose CO, and discuss the potential therapeutic role for CO as part of routine anesthetic management.

The Carbon monoxide releasing molecule ALF-186 mediates anti-inflammatory and neuroprotective effects via the soluble guanylate cyclase ß1 in rats' retinal ganglion cells after ischemia and reperfusion injury

BACKGROUND

The endogenously produced gaseous molecule carbon monoxide is able to promote organ protection after ischemia-reperfusion injuries (IRI). The impact of carbon monoxide releasing molecules (CORM) regarding inflammation in neuronal tissues has not been studied in detail. In this investigation, we aimed to analyze the effects of the CORM ALF-186 on neuro-inflammation and hypothesized that the soluble guanylate cyclase (sGC) is playing a decisive role.

METHODS

Retinal ischemia-reperfusion injury was performed for 60 min in Sprague-Dawley rats. Thereafter, the CORM ALF-186 (10 mg/kg) in the presence or absence of the sGC inhibitor ODQ was injected via a tail vein. Retinal tissue was harvested 24 h later to analyze mRNA or protein expression of sGC-β1 subunit, transcription factors NF-κB and CREB, the inflammatory cytokines TNF-α and IL-6, as well as the heat shock proteins (HSP) HSP-70 and HSP-90. Immunohistochemistry was performed on frozen sections of the retina. The overall neuroprotective effect of ALF-186 was assessed by counting fluorogold-pre-labeled retinal ganglion cells (RGC) 7 days after IRI.

RESULTS

Ischemia-reperfusion mediated loss of vital RGC was attenuated by the administration of ALF-186 after injury. ALF-186 treatment after IRI induced sGC-ß1 leading to a decreased NF-κB and CREB phosphorylation. Consecutively, ALF-186 mitigated IRI induced TNF-α and IL-6 expression in the retina and in the rats' serum. Moreover, ALF-186 attenuated heat shock protein 70 (Hsp-70) while increasing Hsp-90. The sGC-inhibitor ODQ attenuated the anti-inflammatory effects of ALF-186 and increased retinal loss of ganglion cells. These results were confirmed by immunohistochemistry.

CONCLUSION

The CORM ALF-186 protected RGC from IRI induced loss. Furthermore, ALF-186 reduced IRI mediated neuroinflammation in the retina and in the serum by activating sGC. Inhibition of sGC stopped the beneficial and protective effects of ALF-186. ALF-186 may present a promising therapeutic alternative in treating inflammation after neuronal IRI.

The role of carbon monoxide and heme oxygenase in the prevention of sickle cell disease vaso-occlusive crises

Sickle Cell Disease (SCD) is a painful, lifelong hemoglobinopathy inherited as a missense point mutation in the hemoglobin (Hb) beta-globin gene. This disease has significant impact on quality of life and mortality, thus a substantial medical need exists to reduce the vaso-occlusive crises which underlie the pathophysiology of the disease. The concept that a gaseous molecule may exert biological function has been well known for over one hundred years. Carbon monoxide (CO), although studied in SCD for over 50 years, has recently emerged as a powerful cytoprotective biological response modifier capable of regulating a host of physiologic and therapeutic processes that, at low concentrations, exerts key physiological functions in various models of tissue inflammation and injury. CO is physiologically generated by the metabolism of heme by the heme oxygenase enzymes and is measurable in blood. A substantial amount of preclinical and clinical data with CO have been generated, which provide compelling support for CO as a potential therapeutic in a number of pathological conditions. Data underlying the therapeutic mechanisms of CO, including in SCD, have been generated by a plethora of in vitro and preclinical studies including multiple SCD mouse models. These data show CO to have key signaling impacts on a host of metallo-enzymes as well as key modulating genes that in sum, result in significant anti-inflammatory, anti-oxidant and anti-apoptotic effects as well as vasodilation and anti-adhesion of cells to the endothelium resulting in preservation of vascular flow. CO may also have a role as an anti-polymerization HbS agent. In addition, considerable scientific data in the non-SCD literature provide evidence for a beneficial impact of CO on cerebrovascular complications, suggesting that in SCD, CO could potentially limit these highly problematic neurologic outcomes. Research is needed and hopefully forthcoming, to carefully elucidate the safety and benefits of this potential therapy across the age spectrum of patients impacted by the host of pathophysiological complications of this devastating disease.

Carbon Monoxide Improves Efficacy of Mesenchymal Stromal Cells During Sepsis by Production of Specialized Proresolving Lipid Mediators

Supplemental Digital Content is available in the text.

Objectives:

Mesenchymal stromal cells are being investigated as a cell-based therapy for a number of disease processes, with promising results in animal models of systemic inflammation and sepsis. Studies are ongoing to determine ways to further improve the therapeutic potential of mesenchymal stromal cells. A gas molecule that improves outcome in experimental sepsis is carbon monoxide. We hypothesized that preconditioning of mesenchymal stromal cells with carbon monoxide ex vivo would promote further therapeutic benefit when cells are administered in vivo after the onset of polymicrobial sepsis in mice.

Design:

Animal study and primary cell culture.

Setting:

Laboratory investigation.

Subjects:

BALB/c mice.

Interventions:

Polymicrobial sepsis was induced by cecal ligation and puncture. Mesenchymal stromal cells, mesenchymal stromal cells-conditioned with carbon monoxide, fibroblasts, or fibroblasts-conditioned with carbon monoxide were delivered by tail vein injections to septic mice. The mice were assessed for survival, bacterial clearance, and the inflammatory response during sepsis in each of the groups. Mesenchymal stromal cells were also assessed for their ability to promote bacterial phagocytosis by neutrophils, the production of specialized proresolving lipid mediators, and their importance for mesenchymal stromal cells function using gene silencing.

Measurements and Main Results:

Ex vivo preconditioning with carbon monoxide allowed mesenchymal stromal cells to be administered later after the onset of sepsis (6 hr), and yet maintain their therapeutic effect with increased survival. Carbon monoxide preconditioned mesenchymal stromal cells were also able to alleviate organ injury, improve bacterial clearance, and promote the resolution of inflammation. Mesenchymal stromal cells exposed to carbon monoxide, with docosahexaenoic acid substrate, produced specialized proresolving lipid mediators, particularly D-series resolvins, which promoted survival. Silencing of lipoxygenase pathways (5-lipoxygenase and 12/15-lipoxygenase), which are important enzymes for specialized proresolving lipid mediator biosynthesis, resulted in a loss of therapeutic benefit bestowed on mesenchymal stromal cells by carbon monoxide.

Conclusions:

Taken together, these data suggest that production of specialized proresolving lipid mediators contribute to improved mesenchymal stromal cell efficacy when exposed to carbon monoxide, resulting in an improved therapeutic response during sepsis.

Ultraviolet-A1 irradiation therapy for systemic lupus erythematosus

Systemic lupus erythematosus (lupus, SLE) is a chronic autoimmune disease characterized by the production of autoantibodies, which bind to antigens and are deposited within tissues to fix complement, resulting in widespread systemic inflammation. The studies presented herein are consistent with hyperpolarized, adenosine triphosphate (ATP)-deficient mitochondria being central to the disease process. These hyperpolarized mitochondria resist the depolarization required for activation-induced apoptosis. The mitochondrial ATP deficits add to this resistance to apoptosis and also reduce the macrophage energy that is needed to clear apoptotic bodies. In both cases, necrosis, the alternative pathway of cell death, results. Intracellular constituents spill into the blood and tissues, eliciting inflammatory responses directed at their removal. What results is “autoimmunity.” Ultraviolet (UV)-A1 photons have the capacity to remediate this aberrancy. Exogenous exposure to low-dose, full-body, UV-A1 radiation generates singlet oxygen. Singlet oxygen has two major palliative actions in patients with lupus and the UV-A1 photons themselves have several more. Singlet oxygen depolarizes the hyperpolarized mitochondrion, triggering non-ATP-dependent apoptosis that deters necrosis. Next, singlet oxygen activates the gene encoding heme oxygenase (HO-1), a major governor of systemic homeostasis. HO-1 catalyzes the degradation of the oxidant heme into biliverdin (converted to bilirubin), Fe, and carbon monoxide (CO), the first three of these exerting powerful antioxidant effects, and in conjunction with a fourth, CO, protecting against injury to the coronary arteries, the central nervous system, and the lungs. The UV-A1 photons themselves directly attenuate disease in lupus by reducing B cell activity, preventing the suppression of cell-mediated immunity, slowing an epigenetic progression toward SLE, and ameliorating discoid and subacute cutaneous lupus. Finally, a combination of these mechanisms reduces levels of anticardiolipin antibodies and protects during lupus pregnancy. Capping all of this is that UV-A1 irradiation is an essentially innocuous, highly manageable, and comfortable therapeutic agency.

Differential Effects of CORM-2 and CORM-401 in Murine Intestinal Epithelial MODE-K Cells under Oxidative Stress

Carbon monoxide (CO)-releasing molecules (CO-RMs) are intensively studied to provide cytoprotective and anti-inflammatory effects of CO in inflammatory conditions including intestinal inflammation. The water-soluble CORM-A1 reduced apoptosis and NADPH oxidase (NOX)-derived reactive oxygen species (ROS) induced by tumor necrosis factor (TNF)-α/cycloheximide (CHX) in mouse MODE-K intestinal epithelial cells (IECs), without influencing TNF-α/CHX-induced mitochondrial superoxide anion (O2•–). The aim of the present study in the same model was to comparatively investigate the influence of lipid-soluble CORM-2 and water-soluble CORM-401, shown in vitro to release more CO under oxidative conditions. CORM-2 abolished TNF-α/CHX-induced total cellular ROS whereas CORM-401 partially reduced it, both partially reducing TNF-α/CHX-induced cell death. Only CORM-2 increased mitochondrial O2•– production after 2 h of incubation. CORM-2 reduced TNF-α/CHX-, rotenone- and antimycin-A-induced mitochondrial O2•– production; CORM-401 only reduced the effect of antimycin-A. Co-treatment with CORM-401 during 1 h exposure to H₂O₂ reduced H₂O₂ (7.5 mM)-induced ROS production and cell death, whereas CORM-2 did not. The study illustrates the importance of the chemical characteristics of different CO-RMs. The lipid solubility of CORM-2 might contribute to its interference with TNF-α/CHX-induced mitochondrial ROS signaling, at least in mouse IECs. CORM-401 is more effective than other CO-RMs under H₂O₂-induced oxidative stress conditions.

Carbon monoxide incompletely prevents isoflurane-induced defects in murine neurodevelopment

BACKGROUND

Commonly used anesthetics have been shown to disrupt neurodevelopment in preclinical models. It has been proposed that such anesthesia-induced neurotoxicity is mediated by apoptotic neurodegeneration in the immature brain. Low dose carbon monoxide (CO) exerts cytoprotective properties and we have previously demonstrated that CO inhibits isoflurane-induced apoptosis in the developing murine brain. Here we utilized anti-apoptotic concentrations of CO to delineate the role of apoptotic neurodegeneration in anesthesia-induced neurotoxicity by assessing the effect of CO on isoflurane-induced defects in neurodevelopment.

METHODS

C57Bl/6 mouse pups underwent 1-hour exposure to 0ppm (air), 5ppm, or 100ppm CO in air with or without isoflurane on postnatal day 7. Cohorts were evaluated 5-7weeks post exposure with T-maze cognitive testing followed by social behavior assessment. Brain size, whole brain cellular content, and neuronal density in primary somatosensory cortex and hippocampal CA3 region were measured as secondary outcomes 1-week or 5-7weeks post exposure along with 7-day old, unexposed controls.

RESULTS

Isoflurane impaired memory acquisition and resulted in abnormal social behavior. Low concentration CO abrogated anesthetic-induced defects in memory acquisition, however, it also resulted in impaired spatial reference memory and social behavior abnormalities. Changes in brain size, cellular content, and neuronal density over time related to the age of the animal and were unaffected by either isoflurane or CO.

CONCLUSIONS

Anti-apoptotic concentrations of CO incompletely prevented isoflurane-induced defects in neurodevelopment, lacked concentration-dependent effects, and only provided protection in certain domains suggesting that anesthesia-related neurotoxicity is not solely mediated by activation of the mitochondrial apoptosis pathway.

Differential Effects of CORM-2 and CORM-401 in Murine Intestinal Epithelial MODE-K Cells under Oxidative Stress

Carbon monoxide (CO)-releasing molecules (CO-RMs) are intensively studied to provide cytoprotective and anti-inflammatory effects of CO in inflammatory conditions including intestinal inflammation. The water-soluble CORM-A1 reduced apoptosis and NADPH oxidase (NOX)-derived reactive oxygen species (ROS) induced by tumor necrosis factor (TNF)-α/cycloheximide (CHX) in mouse MODE-K intestinal epithelial cells (IECs), without influencing TNF-α/CHX-induced mitochondrial superoxide anion ([Formula: see text]). The aim of the present study in the same model was to comparatively investigate the influence of lipid-soluble CORM-2 and water-soluble CORM-401, shown in vitro to release more CO under oxidative conditions. CORM-2 abolished TNF-α/CHX-induced total cellular ROS whereas CORM-401 partially reduced it, both partially reducing TNF-α/CHX-induced cell death. Only CORM-2 increased mitochondrial [Formula: see text] production after 2 h of incubation. CORM-2 reduced TNF-α/CHX-, rotenone- and antimycin-A-induced mitochondrial [Formula: see text] production; CORM-401 only reduced the effect of antimycin-A. Co-treatment with CORM-401 during 1 h exposure to H₂O₂ reduced H₂O₂ (7.5 mM)-induced ROS production and cell death, whereas CORM-2 did not. The study illustrates the importance of the chemical characteristics of different CO-RMs. The lipid solubility of CORM-2 might contribute to its interference with TNF-α/CHX-induced mitochondrial ROS signaling, at least in mouse IECs. CORM-401 is more effective than other CO-RMs under H₂O₂-induced oxidative stress conditions.

Carbon monoxide and anesthesia-induced neurotoxicity

The majority of commonly used anesthetic agents induce widespread neuronal degeneration in the developing mammalian brain. Downstream, the process appears to involve activation of the oxidative stress-associated mitochondrial apoptosis pathway. Targeting this pathway could result in prevention of anesthetic toxicity in the immature brain. Carbon monoxide (CO) is a gas that exerts biological activity in the developing brain and low dose exposures have the potential to provide neuroprotection. In recent work, low concentration CO exposures limited isoflurane-induced neuronal apoptosis in a dose-dependent manner in newborn mice and modulated oxidative stress within forebrain mitochondria. Because infants and children are routinely exposed to low levels of CO during low-flow general endotracheal anesthesia, such anti-oxidant and pro-survival cellular effects are clinically relevant. Here we provide an overview of anesthesia-related CO exposure, discuss the biological activity of low concentration CO, detail the effects of CO in the brain during development, and provide evidence for CO-mediated inhibition of anesthesia-induced neurotoxicity.

Mitochondria and carbon monoxide: cytoprotection and control of cell metabolism - a role for Ca(2+) ?

Carbon monoxide (CO) is an endogenously produced gasotransmitter with important biological functions: anti-inflammation, anti-apoptosis, vasomodulation and cell metabolism modulation. The most recognized cellular target for CO is the mitochondria. Physiological concentrations of CO generate mitochondrial reactive oxygen species (ROS), which are signalling molecules for CO-induced pathways. Indeed, small amounts of ROS promote cytoprotection by a preconditioning effect. Furthermore, CO prevents cell death by limiting mitochondrial membrane permeabilization, which inhibits the release of pro-apoptotic factors into the cytosol; both events are ROS dependent. CO also increases the ability of mitochondria to take up Ca(2+) . Mitochondrial metabolism is modulated by CO, namely by increasing TCA cycle rate, oxidative phosphorylation and mitochondrial biogenesis, which, in turn, increases ATP production. CO's modulation of metabolism might be important for cellular response to diseases, namely cancer and ischaemic diseases. Finally, another cytoprotective role of CO involves the control of Ca(2+) channels. By limiting the activity of T-type and L-type Ca(2+) channels, CO prevents excitotoxicity-induced cell death and modulates cell proliferation. Several questions concerning Ca(2+) signalling, mitochondria and CO can be asked, for instance whether CO modulation of cell metabolism would be dependent on the mitochondrial Ca(2+) uptake capacity, since small amounts of Ca(2+) can increase mitochondrial metabolism. Whether CO controls Ca(2+) communication between mitochondria and endoplasmic reticulum is another open field of research. In summary, CO emerges as a key gasotransmitter in the control of several cellular functions of mitochondria: metabolism, cell death and Ca(2+) signalling.

Paracrine effect of carbon monoxide - astrocytes promote neuroprotection through purinergic signaling in mice

The neuroprotective role of carbon monoxide (CO) has been studied in a cell-autonomous mode. Herein, a new concept is disclosed - CO affects astrocyte-neuron communication in a paracrine manner to promote neuroprotection. Neuronal survival was assessed when co-cultured with astrocytes that had been pre-treated or not with CO. The CO-pre-treated astrocytes reduced neuronal cell death, and the cellular mechanisms were investigated, focusing on purinergic signaling. CO modulates astrocytic metabolism and extracellular ATP content in the co-culture medium. Moreover, several antagonists of P1 adenosine and P2 ATP receptors partially reverted CO-induced neuroprotection through astrocytes. Likewise, knocking down expression of the neuronal P1 adenosine receptor A2A-R (encoded by Adora2a) reverted the neuroprotective effects of CO-exposed astrocytes. The neuroprotection of CO-treated astrocytes also decreased following prevention of ATP or adenosine release from astrocytic cells and inhibition of extracellular ATP metabolism into adenosine. Finally, the neuronal downstream event involves TrkB (also known as NTRK2) receptors and BDNF. Pharmacological and genetic inhibition of TrkB receptors reverts neuroprotection triggered by CO-treated astrocytes. Furthermore, the neuronal ratio of BDNF to pro-BDNF increased in the presence of CO-treated astrocytes and decreased whenever A2A-R expression was silenced. In summary, CO prevents neuronal cell death in a paracrine manner by targeting astrocytic metabolism through purinergic signaling.

Carbon Monoxide Releasing Molecule-A1 (CORM-A1) Improves Neurogenesis: Increase of Neuronal Differentiation Yield by Preventing Cell Death

Cerebral ischemia and neurodegenerative diseases lead to impairment or death of neurons in the central nervous system. Stem cell based therapies are promising strategies currently under investigation. Carbon monoxide (CO) is an endogenous product of heme degradation by heme oxygenase (HO) activity. Administration of CO at low concentrations produces several beneficial effects in distinct tissues, namely anti-apoptotic and anti-inflammatory. Herein the CO role on modulation of neuronal differentiation was assessed. Three different models with increasing complexity were used: human neuroblastoma SH-S5Y5 cell line, human teratocarcinoma NT2 cell line and organotypic hippocampal slice cultures (OHSC). Cell lines were differentiated into post-mitotic neurons by treatment with retinoic acid (RA) supplemented with CO-releasing molecule A1 (CORM-A1). CORM-A1 positively modulated neuronal differentiation, since it increased final neuronal production and enhanced the expression of specific neuronal genes: Nestin, Tuj1 and MAP2. Furthermore, during neuronal differentiation process, there was an increase in proliferative cell number (ki67 mRNA expressing cells) and a decrease in cell death (lower propidium iodide (PI) uptake, limitation of caspase-3 activation and higher Bcl-2 expressing cells). CO supplementation did not increase the expression of RA receptors. In the case of SH-S5Y5 model, small amounts of reactive oxygen species (ROS) generation emerges as important signaling molecules during CO-promoted neuronal differentiation. CO's improvement of neuronal differentiation yield was validated using OHSC as ex vivo model. CORM-A1 treatment of OHSC promoted higher levels of cells expressing the neuronal marker Tuj1. Still, CORM-A1 increased cell proliferation assessed by ki67 expression and also prevented cell death, which was followed by increased Bcl-2 expression, decreased levels of active caspase-3 and PI uptake. Likewise, ROS signaling emerged as key factors in CO's increasing number of differentiated neurons in OHSC. In conclusion, CO's increasing number of differentiated neurons is a novel biological role disclosed herein. CO improves neuronal yield due to its capacity to reduce cell death, promoting an increase in proliferative population. However, one cannot disregard a direct CO's effect on specific cellular processes of neuronal differentiation. Further studies are needed to evaluate how CO can potentially modulate cell mechanisms involved in neuronal differentiation. In summary, CO appears as a promising therapeutic molecule to stimulate endogenous neurogenesis or to improve in vitro neuronal production for cell therapy strategies.

Synaptic signalling and its interface with neuropathologies: snapshots from the past, present and future

This 'Past to Future' Review as part of the 60th anniversary year of the Journal of Neurochemistry focuses on synaptic transmission and associated signalling, and seeks to identify seminal progress in neurochemistry over the last 10 years which has advanced our understanding of neuronal communication in brain. The approach adopted analyses neurotransmitters on a case by case basis (i.e. amino acids, monoamines, acetylcholine, neuropeptides, ATP/purines and gasotransmitters) to highlight novel findings that have changed the way we view each type of transmitter, to explore commonalities and interactions, and to note how new insights have changed the way we view the biology of degenerative, psychiatric and behavioural conditions. Across all transmitter systems there was remarkable growth in the identification of targets likely to provide therapeutic benefit and which undoubtedly was driven by the elucidation of circuit function and new vistas of synaptic signalling. There has been an increasing trend to relate signalling to disease, notably for Alzheimer's and Parkinson's disease and related conditions, and which has occurred for each transmitter family. Forebrain circuitry and tonic excitatory control have been the centre of great attention yielding novel findings that will impact upon cognitive, emotional and addictive behaviours. Other impressive insights focus on gasotransmitters integrating activity as volume transmitters. Exciting developments in how serotonin, cholinergic, l-glutamate, galanin and adenosine receptors and their associated signalling can be beneficially targeted should underpin the development of new therapies. Clearly integrated, multifaceted neurochemistry has changed the way we view synaptic signalling and its relevance to pathobiology. Highlighted are important advances in synaptic signalling over the last decade in the Journal of Neurochemistry. Across all transmitter systems elucidation of circuit function, and notably molecular insights, have underpinned remarkable growth in the identification of targets likely to provide therapeutic benefit in neuropathologies. Another commonality was wide interest in forebrain circuitry and its tonic excitatory control. Increasingly observations relate to signalling in disease and behavioural conditions. This article is part of the 60th Anniversary special issue.

Mitochondrial Quality Control as a Therapeutic Target

In addition to oxidative phosphorylation (OXPHOS), mitochondria perform other functions such as heme biosynthesis and oxygen sensing and mediate calcium homeostasis, cell growth, and cell death. They participate in cell communication and regulation of inflammation and are important considerations in aging, drug toxicity, and pathogenesis. The cell's capacity to maintain its mitochondria involves intramitochondrial processes, such as heme and protein turnover, and those involving entire organelles, such as fusion, fission, selective mitochondrial macroautophagy (mitophagy), and mitochondrial biogenesis. The integration of these processes exemplifies mitochondrial quality control (QC), which is also important in cellular disorders ranging from primary mitochondrial genetic diseases to those that involve mitochondria secondarily, such as neurodegenerative, cardiovascular, inflammatory, and metabolic syndromes. Consequently, mitochondrial biology represents a potentially useful, but relatively unexploited area of therapeutic innovation. In patients with genetic OXPHOS disorders, the largest group of inborn errors of metabolism, effective therapies, apart from symptomatic and nutritional measures, are largely lacking. Moreover, the genetic and biochemical heterogeneity of these states is remarkably similar to those of certain acquired diseases characterized by metabolic and oxidative stress and displaying wide variability. This biologic variability reflects cell-specific and repair processes that complicate rational pharmacological approaches to both primary and secondary mitochondrial disorders. However, emerging concepts of mitochondrial turnover and dynamics along with new mitochondrial disease models are providing opportunities to develop and evaluate mitochondrial QC-based therapies. The goals of such therapies extend beyond amelioration of energy insufficiency and tissue loss and entail cell repair, cell replacement, and the prevention of fibrosis. This review summarizes current concepts of mitochondria as disease elements and outlines novel strategies to address mitochondrial dysfunction through the stimulation of mitochondrial biogenesis and quality control.

Effect of carbon monoxide on gene expression in cerebrocortical astrocytes: Validation of reference genes for quantitative real-time PCR

Quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR) is a widely used technique to characterize changes in gene expression in complex cellular and tissue processes, such as cytoprotection or inflammation. The accurate assessment of changes in gene expression depends on the selection of adequate internal reference gene(s). Carbon monoxide (CO) affects several metabolic pathways and de novo protein synthesis is crucial in the cellular responses to this gasotransmitter. Herein a selection of commonly used reference genes was analyzed to identify the most suitable internal control genes to evaluate the effect of CO on gene expression in cultured cerebrocortical astrocytes. The cells were exposed to CO by treatment with CORM-A1 (CO releasing molecule A1) and four different algorithms (geNorm, NormFinder, Delta Ct and BestKeeper) were applied to evaluate the stability of eight putative reference genes. Our results indicate that Gapdh (glyceraldehyde-3-phosphate dehydrogenase) together with Ppia (peptidylpropyl isomerase A) is the most suitable gene pair for normalization of qRT-PCR results under the experimental conditions used. Pgk1 (phosphoglycerate kinase 1), Hprt1 (hypoxanthine guanine phosphoribosyl transferase I), Sdha (Succinate Dehydrogenase Complex, Subunit A), Tbp (TATA box binding protein), Actg1 (actin gamma 1) and Rn18s (18S rRNA) genes presented less stable expression profiles in cultured cortical astrocytes exposed to CORM-A1 for up to 60 min. For validation, we analyzed the effect of CO on the expression of Bdnf and bcl-2. Different results were obtained, depending on the reference genes used. A significant increase in the expression of both genes was found when the results were normalized with Gapdh and Ppia, in contrast with the results obtained when the other genes were used as reference. These findings highlight the need for a proper and accurate selection of the reference genes used in the quantification of qRT-PCR results in studies on the effect of CO in gene expression.

Microglia regulate blood clearance in subarachnoid hemorrhage by heme oxygenase-1

Subarachnoid hemorrhage (SAH) carries a 50% mortality rate. The extravasated erythrocytes that surround the brain contain heme, which, when released from damaged red blood cells, functions as a potent danger molecule that induces sterile tissue injury and organ dysfunction. Free heme is metabolized by heme oxygenase (HO), resulting in the generation of carbon monoxide (CO), a bioactive gas with potent immunomodulatory capabilities. Here, using a murine model of SAH, we demonstrated that expression of the inducible HO isoform (HO-1, encoded by Hmox1) in microglia is necessary to attenuate neuronal cell death, vasospasm, impaired cognitive function, and clearance of cerebral blood burden. Initiation of CO inhalation after SAH rescued the absence of microglial HO-1 and reduced injury by enhancing erythrophagocytosis. Evaluation of correlative human data revealed that patients with SAH have markedly higher HO-1 activity in cerebrospinal fluid (CSF) compared with that in patients with unruptured cerebral aneurysms. Furthermore, cisternal hematoma volume correlated with HO-1 activity and cytokine expression in the CSF of these patients. Collectively, we found that microglial HO-1 and the generation of CO are essential for effective elimination of blood and heme after SAH that otherwise leads to neuronal injury and cognitive dysfunction. Administration of CO may have potential as a therapeutic modality in patients with ruptured cerebral aneurysms.

Diverse mechanisms underlying the regulation of ion channels by carbon monoxide

Carbon monoxide (CO) is firmly established as an important, physiological signalling molecule as well as a potent toxin. Through its ability to bind metal-containing proteins, it is known to interfere with a number of intracellular signalling pathways, and such actions can account for its physiological and pathological effects. In particular, CO can modulate the intracellular production of reactive oxygen species, NO and cGMP levels, as well as regulate MAPK signalling. In this review, we consider ion channels as more recently discovered effectors of CO signalling. CO is now known to regulate a growing number of different ion channel types, and detailed studies of the underlying mechanisms of action are revealing unexpected findings. For example, there are clear areas of contention surrounding its ability to increase the activity of high conductance, Ca(2+) -sensitive K(+) channels. More recent studies have revealed the ability of CO to inhibit T-type Ca(2+) channels and have unveiled a novel signalling pathway underlying tonic regulation of this channel. It is clear that the investigation of ion channels as effectors of CO signalling is in its infancy, and much more work is required to fully understand both the physiological and the toxic actions of this gas. Only then can its emerging use as a therapeutic tool be fully and safely exploited.

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.

Oxidative modulation of K+ channels in the central nervous system in neurodegenerative diseases and aging

SIGNIFICANCE

Oxidative stress and damage are well-established components of neurodegenerative diseases, contributing to neuronal death during disease progression. Here, we consider key K(+) channels as target proteins that can undergo oxidative modulation, describe what is understood about how this influences disease progression, and consider regulation of these channels by gasotransmitters as a means of cellular protection.

RECENT ADVANCES

Oxidative regulation of the delayed rectifier Kv2.1 and the Ca(2+)- and voltage-sensitive BK channel are established, but recent studies contest how their redox sensitivity contributes to altered excitability, progression of neurodegenerative diseases, and healthy aging.

CRITICAL ISSUES

Both Kv2.1 and BK channels have recently been established as target proteins for regulation by the gasotransmitters carbon monoxide and hydrogen sulfide. Establishing the molecular basis of such regulation, and exactly how this influences excitability and vulnerability to apoptotic cell death will determine whether such regulation can be exploited for therapeutic benefit.

FUTURE DIRECTIONS

Developing a more comprehensive picture of the oxidative modulation of K(+) channels (and, indeed, other ion channels) within the central nervous system in health and disease will enable us to better understand processes associated with healthy aging as well as distinct processes underlying progression of neurodegenerative diseases. Advances in the growing understanding of how gasotransmitters can regulate ion channels, including redox-sensitive K(+) channels, are a research priority for this field, and will establish their usefulness in design of future approaches for the treatment of such diseases.

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.

Assessment of mitochondrial protein glutathionylation as signaling for CO pathway

Protein glutathionylation is a posttranslational process that regulates protein function in response to redox cellular changes. Furthermore, carbon monoxide-induced cellular pathways involve reactive oxygen species (ROS) signaling and mitochondrial protein glutathionylation. Herein, it is described a technique to assess mitochondrial glutathionylation due to low concentrations of CO exposure. Mitochondria are isolated from cell culture or tissue, followed by an immunoprecipitation assay, which allows the capture of any glutathionylated mitochondrial protein using a specific antibody coupled to a solid matrix that binds to glutathione antigen. The precipitated protein is further identified and quantified by immunoblotting analysis.