Biological signaling by carbon monoxide and carbon monoxide-releasing molecules

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.

Rational Design of Conjugated Polymers for Photocatalytic CO2 Reduction: Towards Localized CO Production and Macrophage Polarization

Light presents substantial potential in disease treatment, where the development of efficient photocatalysts could enhance the utilization of photocatalytic systems in biomedicine. Here, we devised a novel approach to designing and synthesizing photocatalysts of conjugated polymers for photocatalytic CO2 reduction, relying on a multiple linear regression model built with theoretically calculated descriptors. We established a logarithmic relationship between molecular structure and CO yield and identified the poly(fluorene-co-thiophene) deviant (PFT) as the optimal one. PFT excited a CO regeneration ratio of 231 nmol h-1 in acetonitrile and 46 nmol h-1 in an aqueous solution with a reaction selectivity of 88%. Further advancements were made through the development of liposomes encapsulating PFT for targeted macrophage delivery. By distributing PFT on the liposome membranes, our constructed photocatalytic system efficiently generated CO in situ from surrounding CO2. This localized CO production served as an endogenous signaling molecule, promoting the desirable polarization of macrophages from the M1 to M2 phenotype. Consequently, the M2 cells reduced the secretion of pro-inflammatory cytokines (TNF-α, IL-6, and IL-1β). We also demonstrated the efficacy of our system in treating lipopolysaccharide-induced inflammation of cardiomyocytes under white light irradiation. Moreover, our research provides a comprehensive understanding of the intricate processes involved in CO2 reduction by a combination of theoretical calculations and experimental techniques including transient absorption, femtosecond ultrafast spectroscopy, and in situ infrared spectroscopy. These findings pave the way for further advancements of conjugated polymers and photocatalytic systems in biomedical investigation.

Design and engineering of logic genetic-enzymatic gates based on the activity of the human CYP2C9 enzyme in permeabilized Saccharomyces cerevisiae cells

Gene circuits allow cells to carry out complex functions such as the precise regulation of biological metabolic processes. In this study, we combined, in the yeast S. cerevisiae, genetic regulatory elements with the enzymatic reactions of the human CYP2C9 and its redox partner CPR on luciferin substrates and diclofenac. S. cerevisiae cells were permeabilized and used as enzyme bags in order to host these metabolic reactions. We engineered three different (genetic)-enzymatic basic Boolean gates (YES, NOT, and N-IMPLY). In the YES and N-IMPLY gates, human CYP2C9 was expressed under the galactose-inducible GAL1 promoter. The carbon monoxide releasing molecule CORM-401 was used as an input in the NOT and N-IMPLY gates to impair CYP2C9 activity through inhibition of the Fe+2- heme prosthetic group in the active site of the human enzyme. Our study provides a new approach in designing synthetic bio-circuits and optimizing experimental conditions to favor the heterologous expression of human drug metabolic enzymes over their endogenous counterparts. This new approach will help study precise metabolic attributes of human P450s.

Identification of human circulating factors following remote ischemic conditioning (RIC): Potential impact on stroke

Remote ischemic conditioning (RIC) is a procedure consisting of short cycles of ischemia applied in a limb that activates endogenous protection in distant organs, such as the brain. Despite the promising outcomes of RIC, the biochemical factors governing inter-organ communication remain largely unexplored, particularly in humans. A pilot study on 20 healthy humans was performed to identify potential circulating biochemical factors involved in RIC signalling. Blood was collected before and immediately, 4 and 22 h after the end of RIC. To characterize the responses triggered by RIC, a combination of biochemical and proteomic analysis, along with functional in vitro tests in human cells, were performed. RIC did not alter the levels of nitric oxide, bilirubin and cell-free mitochondrial DNA. In contrast, carboxyhaemoglobin levels increased following RIC at all time points and young subset, suggesting endogenous production of carbon monoxide that is a cytoprotective gasotransmitter. Additionally, the levels of glutathione and cysteinylglycine bound to proteins also increased after RIC, while glutathione catabolism decreased. Plasma proteomic analysis identified overall 828 proteins. Several steps of statistical analysis (Student's t-test, repeated measures ANOVA, with Holm corrected pairwise p-values <0.05 threshold and fold change higher or lower than 100 %) leaded to the identification of 9 proteins with altered circulating levels in response to RIC at 4h and 22h. All 9 proteins are from extracellular space or exosomes, being involved in inflammation, angiogenesis or metabolism control. In addition, RIC-conditioned plasma from young subjects protected microglial cell culture against inflammatory stimuli, indicating an anti-inflammatory effect of RIC. Nevertheless, other functional tests in neurons or endothelial cells had no effect. Overall, we present some evidence for RIC-induced anti-inflammatory and antioxidant responses in healthy human subjects, in particular in young subjects. This study is a first step towards the disclosure of signalling factors involved in RIC-mediated inter-organ communication.

Gas Therapy: Generating, Delivery, and Biomedical Applications

Oxygen (O2), nitric oxide (NO), carbon monoxide (CO), hydrogen sulfide (H2S), and hydrogen (H2) with direct effects, and carbon dioxide (CO2) with complementary effects on the condition of various diseases are known as therapeutic gases. The targeted delivery and in situ generation of these therapeutic gases with controllable release at the site of disease has attracted attention to avoid the risk of gas poisoning and improve their performance in treating various diseases such as cancer therapy, cardiovascular therapy, bone tissue engineering, and wound healing. Stimuli-responsive gas-generating sources and delivery systems based on biomaterials that enable on-demand and controllable release are promising approaches for precise gas therapy. This work highlights current advances in the design and development of new approaches and systems to generate and deliver therapeutic gases at the site of disease with on-demand release behavior. The performance of the delivered gases in various biomedical applications is then discussed.

Carbon monoxide-loaded cell therapy as an exercise mimetic for sarcopenia treatment

Sarcopenia is characterized by loss of muscle strength and muscle mass with aging. The growing number of sarcopenia patients as a result of the aging population has no viable treatment. Exercise maintains muscle strength and mass by increasing peroxisome growth factor activating receptor γ-conjugating factor-1α (PGC-1α) and Akt signaling in skeletal muscle. The present study focused on the carbon monoxide (CO), endogenous activator of PGC-1α and Akt, and investigated the therapeutic potential of CO-loaded red blood cells (CO-RBCs), which is bioinspired from in vivo CO delivery system, as an exercise mimetic for the treatment of sarcopenia. Treatment of C2C12 myoblasts with the CO-donor increased the protein levels of PGC-1α which enhanced mitochondrial biogenesis and energy production. The CO-donor treatment also activated Akt, indicating that CO promotes muscle synthesis. CO levels were significantly elevated in the skeletal muscle of normal mice after intravenous administration of CO-RBCs. Furthermore, CO-RBCs restored the mRNA expression levels of PGC-1α in the skeletal muscle of two experimental sarcopenia mouse models, denervated (Den) and hindlimb unloading (HU) models. CO-RBCs also restored muscle mass in Den mice by activating Akt signaling and suppressing the muscle atrophy factors myostatin and atrogin-1, and oxidative stress. Treadmill tests further showed that the reduced running distance in HU mice was significantly restored by CO-RBC administration. These findings suggest that CO-RBCs have potential as an exercise mimetic for sarcopenia treatment.

An orally active carbon monoxide-releasing molecule enhances beneficial gut microbial species to combat obesity in mice

Carbon monoxide (CO), a gaseous signaling molecule, has shown promise in preventing body weight gain and metabolic dysfunction induced by high fat diet (HFD), but the mechanisms underlying these effects are largely unknown. An essential component in response to HFD is the gut microbiome, which is significantly altered during obesity and represents a target for developing new therapeutic interventions to fight metabolic diseases. Here, we show that CO delivered to the gut by oral administration with a CO-releasing molecule (CORM-401) accumulates in faeces and enriches a variety of microbial species that were perturbed by a HFD regimen. Notably, Akkermansia muciniphila, which exerts salutary metabolic effects in mice and humans, was strongly depleted by HFD but was the most abundant gut species detected after CORM-401 treatment. Analysis of bacterial transcripts revealed a restoration of microbial functional activity, with partial or full recovery of the Krebs cycle, β-oxidation, respiratory chain and glycolysis. Mice treated with CORM-401 exhibited normalization of several plasma and fecal metabolites that were disrupted by HFD and are dependent on Akkermansia muciniphila's metabolic activity, including indoles and tryptophan derivatives. Finally, CORM-401 treatment led to an improvement in gut morphology as well as reduction of inflammatory markers in colon and cecum and restoration of metabolic profiles in these tissues. Our findings provide therapeutic insights on the efficacy of CO as a potential prebiotic to combat obesity, identifying the gut microbiota as a crucial target for CO-mediated pharmacological activities against metabolic disorders.

Beneficial Effects of Oral Carbon Monoxide on Doxorubicin-Induced Cardiotoxicity

BACKGROUND

Doxorubicin and other anthracyclines are crucial cancer treatment drugs. However, they are associated with significant cardiotoxicity, severely affecting patient care and limiting dosage and usage. Previous studies have shown that low carbon monoxide (CO) concentrations protect against doxorubicin toxicity. However, traditional methods of CO delivery pose complex challenges for daily administration, such as dosing and toxicity. To address these challenges, we developed a novel oral liquid drug product containing CO (HBI-002) that can be easily self-administered by patients with cancer undergoing doxorubicin treatment, resulting in CO being delivered through the upper gastrointestinal tract.

METHODS AND RESULTS

HBI-002 was tested in a murine model of doxorubicin cardiotoxicity in the presence and absence of lung or breast cancer. The mice received HBI-002 twice daily before doxorubicin administration and experienced increased carboxyhemoglobin levels from a baseline of ≈1% to 7%. Heart tissue from mice treated with HBI-002 had a 6.3-fold increase in CO concentrations and higher expression of the cytoprotective enzyme heme oxygenase-1 compared with placebo control. In both acute and chronic doxorubicin toxicity scenarios, HBI-002 protected the heart from cardiotoxic effects, including limiting tissue damage and cardiac dysfunction and improving survival. In addition, HBI-002 did not compromise the efficacy of doxorubicin in reducing tumor volume, but rather enhanced the sensitivity of breast 4T1 cancer cells to doxorubicin while simultaneously protecting cardiac function.

CONCLUSIONS

These findings strongly support using HBI-002 as a cardioprotective agent that maintains the therapeutic benefits of doxorubicin cancer treatment while mitigating cardiac damage.

Sulfur assimilation using gaseous carbonyl sulfide by the soil fungus Trichoderma harzianum

Fungi have the capacity to assimilate a diverse range of both inorganic and organic sulfur compounds. It has been recognized that all sulfur sources taken up by fungi are in soluble forms. In this study, we present evidence that fungi can utilize gaseous carbonyl sulfide (COS) for the assimilation of a sulfur compound. We found that the filamentous fungus Trichoderma harzianum strain THIF08, which has constitutively high COS-degrading activity, was able to grow with COS as the sole sulfur source. Cultivation with 34S-labeled COS revealed that sulfur atom from COS was incorporated into intracellular metabolites such as glutathione and ergothioneine. COS degradation by strain THIF08, in which as much of the moisture derived from the agar medium as possible was removed, indicated that gaseous COS was taken up directly into the cell. Escherichia coli transformed with a COS hydrolase (COSase) gene, which is clade D of the β-class carbonic anhydrase subfamily enzyme with high specificity for COS but low activity for CO2 hydration, showed that the COSase is involved in COS assimilation. Comparison of sulfur metabolites of strain THIF08 revealed a higher relative abundance of reduced sulfur compounds under the COS-supplemented condition than the sulfate-supplemented condition, suggesting that sulfur assimilation is more energetically efficient with COS than with sulfate because there is no redox change of sulfur. Phylogenetic analysis of the genes encoding COSase, which are distributed in a wide range of fungal taxa, suggests that the common ancestor of Ascomycota, Basidiomycota, and Mucoromycota acquired COSase at about 790-670 Ma.IMPORTANCEThe biological assimilation of gaseous CO2 and N2 involves essential processes known as carbon fixation and nitrogen fixation, respectively. In this study, we found that the fungus Trichoderma harzianum strain THIF08 can grow with gaseous carbonyl sulfide (COS), the most abundant and ubiquitous gaseous sulfur compound, as a sulfur source. When the fungus grew in these conditions, COS was assimilated into sulfur metabolites, and the key enzyme of this assimilation process is COS hydrolase (COSase), which specifically degrades COS. Moreover, the pathway was more energy efficient than the typical sulfate assimilation pathway. COSase genes are widely distributed in Ascomycota, Basidiomycota, and Mucoromycota and also occur in some Chytridiomycota, indicating that COS assimilation is widespread in fungi. Phylogenetic analysis of these genes revealed that the acquisition of COSase in filamentous fungi was estimated to have occurred at about 790-670 Ma, around the time that filamentous fungi transitioned to a terrestrial environment.

Relationship between red blood cell lifespan and endogenous carbon monoxide in the common bottlenose dolphin and beluga

Certain deep-diving marine mammals [i.e., northern elephant seal (Mirounga angustirostris), Weddell seal (Leptonychotes weddellii)] have blood carbon monoxide (CO) levels that are comparable with those of chronic cigarette smokers. Most CO produced in humans is a byproduct of heme degradation, which is released when red blood cells (RBCs) are destroyed. Elevated CO can occur in humans when RBC lifespan decreases. The contribution of RBC turnover to CO concentrations in marine mammals is unknown. Here, we report the first RBC lifespans in two healthy marine mammal species with different diving capacities and heme stores, the shallow-diving bottlenose dolphin (Tursiops truncatus) and deep-diving beluga whale (Delphinapterus leucas), and we relate the lifespans to the levels of CO in blood and breath. The belugas, with high blood heme stores, had the longest mean RBC lifespan compared with humans and bottlenose dolphins. Both cetacean species were found to have three times higher blood CO content compared with humans. The estimated CO production rate from heme degradation indicates some marine mammals may have additional mechanisms for CO production, or delay CO removal from the body, potentially from long-duration breath-holds.NEW & NOTEWORTHY This is the first study to determine the red blood cell lifespan in a marine mammal species. High concentrations of carbon monoxide (CO) were found in the blood of bottlenose dolphins and in the blood and breath of belugas compared with healthy humans. Red blood cell turnover accounted for these high levels in bottlenose dolphins, but there may be alternative mechanisms of endogenous CO production that are contributing to the CO concentrations observed in belugas.

The FEDBD plasma's quantitative investigation of skin parameters: Skin elasticity, thickness, density, tissue oxygenation, perfusion, and edema

This study used the FEDBD plasma device for skin rejuvenation in animal samples. There were two groups of six male Wistar rats. Before starting the treatment, immediately after the treatment, the fourth week, and the tenth week of follow-up, biometric tests were performed, including moisture level, evaporation from the skin surface, erythema and melanin, skin elasticity and firmness with an MPA9 device and cutometer. The thickness and density of the epidermis and dermis, an essential indicator in rejuvenation, were evaluated with a skin ultrasound device. Also, the level of oxygen, perfusion, and interstitial water (edema) was checked using a Tivita tissue hyperspectral camera at a depth of 6 mm of the skin.

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.

A Review of the Potential of Nuclear Factor [Erythroid-Derived 2]-like 2 Activation in Autoimmune Diseases

An autoimmune disease is the consequence of the immune system attacking healthy cells, tissues, and organs by mistake instead of protecting them. Inflammation and oxidative stress (OS) are well-recognized processes occurring in association with acute or chronic impairment of cell homeostasis. The transcription factor Nrf2 (nuclear factor [erythroid-derived 2]-like 2) is of major importance as the defense instrument against OS and alters anti-inflammatory activities related to different pathological states. Researchers have described Nrf2 as a significant regulator of innate immunity. Growing indications suggest that the Nrf2 signaling pathway is deregulated in numerous diseases, including autoimmune disorders. The advantageous outcome of the pharmacological activation of Nrf2 is an essential part of Nrf2-based chemoprevention and intervention in other chronic illnesses, such as neurodegeneration, cardiovascular disease, autoimmune diseases, and chronic kidney and liver disease. Nevertheless, a growing number of investigations have indicated that Nrf2 is already elevated in specific cancer and disease steps, suggesting that the pharmacological agents developed to mitigate the potentially destructive or transformative results associated with the protracted activation of Nrf2 should also be evaluated. The activators of Nrf2 have revealed an improvement in the progress of OS-associated diseases, resulting in immunoregulatory and anti-inflammatory activities; by contrast, the depletion of Nrf2 worsens disease progression. These data strengthen the growing attention to the biological properties of Nrf2 and its possible healing power on diseases. The evidence supporting a correlation between Nrf2 signaling and the most common autoimmune diseases is reviewed here. We focus on the aspects related to the possible effect of Nrf2 activation in ameliorating pathologic conditions based on the role of this regulator of antioxidant genes in the control of inflammation and OS, which are processes related to the progression of autoimmune diseases. Finally, the possibility of Nrf2 activation as a new drug development strategy to target pathogenesis is proposed.

Tissue Perfusion and Diffusion and Cellular Respiration: Transport and Utilization of Oxygen

This article provides an overview of the journey of inspired oxygen after its uptake across the alveolar-capillary interface, and the interplay among tissue perfusion, diffusion, and cellular respiration in the transport and utilization of oxygen. The critical interactions between oxygen and its facilitative carriers (hemoglobin in red blood cells and myoglobin in muscle cells), and with other respiratory and vasoactive molecules (carbon dioxide, nitric oxide, and carbon monoxide), are emphasized to illustrate how this versatile system dynamically optimizes regional convective transport and diffusive gas exchange. The rates of reciprocal gas exchange in the lung and the periphery must be well-matched and sufficient for meeting the range of energy demands from rest to maximal stress but not excessive as to become toxic. The mobile red blood cells play a vital role in matching tissue perfusion and gas exchange by dynamically regulating the controlled uptake of oxygen and communicating regional metabolic signals across different organs. Intracellular oxygen diffusion and facilitation via myoglobin into the mitochondria, and utilization via electron transport chain and oxidative phosphorylation, are summarized. Physiological and pathophysiological adaptations are briefly described. Dysfunction of any component across this integrated system affects all other components and elicits corresponding structural and functional adaptation aimed at matching the capacities across the entire system and restoring equilibrium under normal and pathological conditions.

Exploring the therapeutic potential of a nano micelle containing a carbon monoxide-releasing molecule for metabolic-associated fatty liver disease by modulating hypoxia-inducible factor-1α

Metabolic-associated fatty liver disease (MAFLD) encompasses a spectrum of chronic liver diseases, including steatohepatitis, cirrhosis, and liver cancer. Despite the increasing prevalence and severity of MAFLD, no approved pharmacological interventions are currently available. Hypoxia-inducible factor-1α (HIF-1α) has emerged as a crucial early mediator in the pathogenesis of MAFLD. Previously, we demonstrated the potent anti-inflammatory properties of the nano-designed carbon monoxide (CO) donor, styrene maleic acid copolymer (SMA) encapsulating CO-releasing molecule (SMA/CORM2), which effectively suppressed HIF-1α in various inflammatory disorders. Here, we investigated the therapeutic potential of SMA/CORM2 in a mouse model of MAFLD induced by a high-fat methionine- and choline-deficient (HF-MCD) diet. Following 4 weeks of HF-MCD diet consumption, we observed pronounced hepatic lipid accumulation accompanied by disrupted lipid metabolism, polarization of macrophages towards the pro-inflammatory M1 phenotype, activation of the NLRP3 inflammasome, and upregulation of the TGF-β fibrosis signaling pathway. Notably, the early and upstream event driving these pathological changes was the upregulation of HIF-1α. Treatment with SMA/CORM2 (10 mg/kg, three times per week) led to a significant increase in CO levels in both the circulation and liver, resulting in remarkable suppression of HIF-1α expression even before the onset of apparent pathological changes induced by the HF-MCD diet. Consequently, SMA/CORM2 administration exerted a significantly protective and therapeutic effect on MAFLD. In vitro studies using hepatocytes treated with high concentrations of fatty acids further supported these findings, as knockdown of HIF-1α using short hairpin RNA (shRNA) elicited similar effects to SMA/CORM2 treatment. Collectively, our results highlight the therapeutic potential of SMA/CORM2 in the management of MAFLD through suppression of HIF-1α. We anticipate that SMA/CORM2, with its ability to modulate HIF-1α expression, may hold promise for future applications in the treatment of MAFLD. STATEMENT OF SIGNIFICANCE: Carbon monoxide (CO) is a crucial gaseous signaling molecule that plays a vital role in maintaining homeostasis and is a potential target for treating many inflammatory diseases. Developing drug delivery systems that can deliver CO stably and target specific tissues is of great interest. Our team previously developed a nano micellar CO donor, SMA/CORM2, which exhibits superior bioavailability to native CORM2 and shows therapeutic potential in many inflammatory disease models. In this study, we showed that SMA/CORM2, through controlled CO release, significantly ameliorated steatohepatitis and liver fibrosis induced by an HF-MCD diet by suppressing an HIF-1α mediated inflammatory cascade. These findings provide new insight into the anti-inflammatory function of CO and a promising approach for controlling metabolic-associated fatty liver disease.

Gasotransmitters in non-alcoholic fatty liver disease: just the tip of the iceberg

Non-alcoholic fatty liver disease (NAFLD) is a clinicopathological syndrome characterized by fatty lesions and fat accumulation in hepatic parenchymal cells, which is in the absence of excessive alcohol consumption or definite liver damage factors. The exact pathogenesis of NAFLD is not fully understood, but it is now recognized that oxidative stress, insulin resistance, and inflammation are essential mechanisms involved in the development and treatment of NAFLD. NAFLD therapy aims to stop, delay or reverse disease progressions, as well as improve the quality of life and clinical outcomes of patients with NAFLD. Gasotransmitters are produced by enzymatic reactions, regulated through metabolic pathways in vivo, which can freely penetrate cell membranes with specific physiological functions and targets. Three gasotransmitters, nitric oxide, carbon monoxide, and hydrogen sulfide have been discovered. Gasotransmitters exhibit the effects of anti-inflammatory, anti-oxidant, vasodilatory, and cardioprotective agents. Gasotransmitters and their donors can be used as new gas-derived drugs and provide new approaches to the clinical treatment of NAFLD. Gasotransmitters can modulate inflammation, oxidative stress, and numerous signaling pathways to protect against NAFLD. In this paper, we mainly review the status of gasotransmitters research on NAFLD. It provides clinical applications for the future use of exogenous and endogenous gasotransmitters for the treatment of NAFLD.

CORM-3 alleviates the intestinal injury in a rodent model of hemorrhage shock and resuscitation: roles of GFAP-positive glia

Hemorrhagic shock and resuscitation (HSR) can induce severe intestinal damages, thereby leading to sepsis and long-term complications including dysbacteriosis and pulmonary injury. The NOD-like receptor protein 3 (NLRP3) inflammasome facilitates inflammation-associated cell recruitment in the gastrointestinal tract, and participates in many inflammatory bowel diseases. Previous studies have shown that exogenous carbon monoxide (CO) exerts neuroprotective effects against pyroptosis after HSR. We aimed to investigate whether carbon monoxide-releasing molecules-3 (CORM-3), an exogenous CO compound, could attenuate HSR-induced intestinal injury and the potential underlying mechanism.Rats were subjected to a HSR model by bleeding and re-infusion. Following resuscitation, 4 mg/kg of CORM-3 was administered intravenously into femoral vein. At 24 h and 7 d after HSR modeling, the pathological changes in intestinal tissues were evaluated by H&E staining. The intestinal pyroptosis, glial fibrillary acidic protein (GFAP)-positive glial pyroptosis, DAO (diamine oxidase) content, intestine tight junction proteins including zonula occludens-1 (ZO-1) and claudin-1 were further detected by immunofluorescence, western blot and chemical assays at 7 d after HSR. CORM-3 administration led to significantly mitigated HSR-induced intestinal injury, aggravation of intestinal pyroptosis indicated by cleaved caspase-1, IL-1β and IL-18, upregulation of GFAP-positive glial pyroptosis, decreased intensity of ZO-1 and claudin-1 in the jejunum, and increased of DAO in the serum. Nigericin, an agonist of NLRP3, significantly reversed the protective effects of CORM-3. CORM-3 alleviates the intestinal barrier dysfunction in a rodent model of HSR, and the potential mechanism may be associated with inhibition of NLRP3-associated pyroptosis. CORM-3 administration could be a promising therapeutic strategy for intestinal injury after hemorrhagic shock.

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.

Polymeric nano-micelle of carbon monoxide donor SMA/CORM2 ameliorates acetaminophen-induced liver injury via suppressing HMGB1/TLR4 signaling pathway

Acetaminophen (APAP) overdose-induced hepatotoxicity is the most common cause of acute liver failure. Excessive generation of reactive oxygen species (ROS) and inflammatory responses are the major causes of necrosis and/or necroptosis of the liver cells. Currently, the treatment options for APAP-induced liver injury are very limited, N-acetylcysteine (NAC) is the only approved drug to treat APAP overdose patients. It is of great necessity to develop new therapeutic strategies. In a previous study, we focused on the anti-oxidative, anti-inflammatory signal molecule carbon monoxide (CO), and developed a nano-micelle encapsulating CO donor, i.e., SMA/CORM2. Administration of SMA/CORM2 to the mice exposed to APAP significantly ameliorated the liver injury and inflammatory process, in which modulating macrophage reprogramming plays a critical role. Along this line, in this study, we investigated the potential effect of SMA/CORM2 on toll-like receptor 4 (TLR4) and high mobility group protein B1 (HMGB1) signaling pathways that are known to be closely involved in many inflammatory responses and necroptosis. In a mouse APAP-induced liver injury model, similar to the previous study, SMA/CORM2 at 10 mg/kg remarkably improved the condition of the liver after injury as evidenced by histological examination and liver function. During the process of liver injury triggered by APAP, TLR4 expression gradually increased over time, and it was significantly upregulated as early as 4 h after APAP exposure, whereas, an increase of HMGB1 was a late-stage event. Notably, SMA/CORM2 treatment suppressed significantly both TLR4 and HMGB1, consequently inhibiting the progression of inflammation and liver injury. Compared to CORM2 without SMA modification (native CORM2) of 1 mg/kg that is equivalent to 10 mg/kg of SMA/CORM2 (the amount of CORM2 in SMA/CORM2 is 10% [w/w]), SMA/CORM2 exhibited a much better therapeutic effect, indicating its superior therapeutic efficacy to native CORM2. These findings revealed that SMA/CORM2 protects against APAP-induced liver injury via mechanisms involving the suppression of TLR4 and HMGB1 signaling pathways. Taking together the results in this study and previous studies, SMA/CORM2 exhibits great therapeutic potential for APAP overdose-induced liver injury, we thus anticipate the clinical application of SMA/CORM2 for the treatment of APAP overdose, as well as other inflammatory diseases.

Glutamine Deficiency Promotes Immune and Endothelial Cell Dysfunction in COVID-19

The coronavirus disease 2019 (COVID-19) pandemic has caused the death of almost 7 million people worldwide. While vaccinations and new antiviral drugs have greatly reduced the number of COVID-19 cases, there remains a need for additional therapeutic strategies to combat this deadly disease. Accumulating clinical data have discovered a deficiency of circulating glutamine in patients with COVID-19 that associates with disease severity. Glutamine is a semi-essential amino acid that is metabolized to a plethora of metabolites that serve as central modulators of immune and endothelial cell function. A majority of glutamine is metabolized to glutamate and ammonia by the mitochondrial enzyme glutaminase (GLS). Notably, GLS activity is upregulated in COVID-19, favoring the catabolism of glutamine. This disturbance in glutamine metabolism may provoke immune and endothelial cell dysfunction that contributes to the development of severe infection, inflammation, oxidative stress, vasospasm, and coagulopathy, which leads to vascular occlusion, multi-organ failure, and death. Strategies that restore the plasma concentration of glutamine, its metabolites, and/or its downstream effectors, in conjunction with antiviral drugs, represent a promising therapeutic approach that may restore immune and endothelial cell function and prevent the development of occlusive vascular disease in patients stricken with COVID-19.

Development of carbon monoxide-releasing molecules conjugated to polysaccharides (glyco-CORMs) for delivering CO during obesity

Metal carbonyls have been developed as carbon monoxide-releasing molecules (CO-RMs) to deliver CO for therapeutic purposes. The manganese-based CORM-401 has been recently reported to exert beneficial effects in obese animals by reducing body weight gain, improving glucose metabolism and reprogramming adipose tissue towards a healthy phenotype. Here, we report on the synthesis and characterization of glyco-CORMs, obtained by grafting manganese carbonyls on dextrans (70 and 40kDa), based on the fact that polysaccharides facilitate the targeting of drugs to adipose tissue. We found that glyco-CORMs efficiently deliver CO to cells in vitro with higher CO accumulation in adipocytes compared to other cell types. Oral administration of two selected glyco-CORMs (5b and 6b) resulted in CO accumulation in various organs, including adipose tissue. In addition, glyco-CORM 6b administered for eight weeks elicited anti-obesity and positive metabolic effects in mice fed a high fat diet. Our study highlights the feasibility of creating carriers with multiple functionalized CO-RMs.

Spectroscopical and Molecular Studies of Four Manganese(I) PhotoCORMs with Bioinspired Ligands Containing Non-Coordinated Phenol Groups

Carbonyl compounds are widely explored in medicinal inorganic chemistry and have drawn attention due to their signaling functions in homeostasis. Carbon-monoxide-releasing molecules (CORMs) were developed with the purpose of keeping the CO inactive until its release in the intracellular environment, considering its biological relevance. However, for therapeutic applications, the mechanisms of photorelease and which electronic and structural variations influence its rates must be fully understood. In this work, four ligands containing a pyridine, a secondary amine, and a phenolic group with different substituents were used to prepare new Mn(I) carbonyl compounds. Structural and physicochemical characterization of these complexes was carried out and confirmed the proposed structures. X-ray diffractometry structures obtained for the four organometallic compounds revealed that the substituents in the phenolic ring promote only negligible distortions in their geometry. Furthermore, UV-Vis and IR kinetics showed the direct dependence of the electron-withdrawing or donating ability of the substituent group, indicating an influence of the phenol ring on the CO release mechanism. These differences in properties were also supported by theoretical studies at the DFT, TD-DFT, and bonding situation analyses (EDA-NOCV). Two methods were used to determine the CO release constants (k_CO,old and k_CO,new), where Mn-HbpaBr (1) had the greatest k_CO by both methods (K_co,old = 2.36 × 10^-3 s^-1 and k_CO,new = 2.37 × 10^-3 s^-1). Carbon monoxide release was also evaluated using the myoglobin assay, indicating the release of 1.248 to 1.827 carbon monoxides upon light irradiation.

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.

Strategies toward Metal-Free Carbon Monoxide Prodrugs: An Update

Carbon monoxide is an important gasotransmitter in mammals, with pleiotropic therapeutic potential against a wide range of human diseases. However, clinical translation of CO is severely hampered by the lack of a reliable CO delivery form. The development of metal-free CO prodrugs is the key to resolving such delivery issues. Over the past three years, some new exciting progress has been made in this field. In this review, we highlight these advances and discuss related issues.

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

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

Ultrafast Widefield Mid-Infrared Photothermal Heterodyne Imaging

Mid-infrared photothermal (MIP) microscopy is a valuable tool for sensitive and fast chemical imaging with high spatial resolution beyond the mid-infrared diffraction limit. The highest sensitivity is usually achieved with heterodyne MIP employing photodetector point-scans and lock-in detection, while the fastest systems use camera-based widefield MIP with pulsed probe light. One challenge is to simultaneously achieve high sensitivity, spatial resolution, and speed in a large field of view. Here, we present widefield mid-infrared photothermal heterodyne (WIPH) imaging, where a digital frequency-domain lock-in (DFdLi) filter is used for simultaneous multiharmonic demodulation of MIP signals recorded by individual camera pixels at frame rates up to 200 kHz. The DFdLi filter enables the use of continuous-wave probe light, which, in turn, eliminates the need for synchronization schemes and allows measuring MIP decay curves. The WIPH approach is characterized by imaging potassium ferricyanide microparticles and applied to detect lipid droplets (alkyne-palmitic acid) in 3T3-L1 fibroblast cells, both in the cell-silent spectral region around 2100 cm^–1 using an external-cavity quantum cascade laser. The system achieved up to 4000 WIPH images per second at a signal-to-noise ratio of 5.52 and 1 μm spatial resolution in a 128 × 128 μm field of view. The technique opens up for real-time chemical imaging of fast processes in biology, medicine, and material science.

Examination of central nervous system by functional observation battery after massive intravenous infusion of carbon monoxide-bound and oxygen-bound hemoglobin vesicles in rats

Carbon monoxide (CO) is known as a toxic gas inducing "CO poisoning", which acutely affects the central nervous system (CNS) and which persistently affects brain functions depending on the exposure time and CO concentration. By contrast, in pathological rodent models, intravenous infusion of CO-bound hemoglobin vesicles (CO-HbV) has shown various beneficial effects such as anti-oxidative and anti-inflammatory reactions. This study assessed effects of CO-HbV infusion on CNS using a functional observation battery, sensory reflexes, grip strength, and landing foot splay measurements. The test fluids were CO-HbV and O₂-bound HbV (O₂-HbV) suspended in saline ([Hb] ​= ​10 ​g/dL), and saline alone for comparison. The rats received either 16 or 32 ​mL/kg of fluid intravenously at 1.5 ​mL/min/kg. Observations were made before infusion, and at 5 ​min, 4, 8, 24, 48 and 72 ​h after infusion. Massive doses of 16 and 32 ​mL/kg respectively corresponded to about 29 and 57% of the whole circulating blood volume (56 ​mL/kg). No toxicological effect was observed in any measurement item for any group in comparison to the control saline infusion group. Histopathological examination of hippocampal tissue at 14 days after infusion showed the number of necrotic cells to be minimal. Results obtained from rats in this experiment suggest that the massive intravenous infusion of CO-HbV yields beneficial anti-oxidative and anti-inflammatory effects without showing CO-poisoning-related symptoms of CNS damage.

Natural flavylium-inspired far-red to NIR-II dyes and their applications as fluorescent probes for biomedical sensing

Fluorescent probes that emit in the far-red (600-700 nm), first near-infrared (NIR-I, 700-900 nm), and second NIR (NIR-II, 900-1700 nm) regions possess unique advantages, including low photodamage and deep penetration into biological samples. Notably, NIR-II optical imaging can achieve tissue penetration as deep as 5-20 mm, which is critical for biomedical sensing and clinical applications. Much research has focused on developing far-red to NIR-II dyes to meet the needs of modern biomedicine. Flavylium compounds are natural colorants found in many flowers and fruits. Flavylium-inspired dyes are ideal platforms for constructing fluorescent probes because of their far-red to NIR emissions, high quantum yields, high molar extinction coefficients, and good water solubilities. The synthetic and structural diversities of flavylium dyes also enable NIR-II probe development, which markedly advance the field of NIR-II in vivo imaging. In the last decade, there have been huge developments in flavylium-inspired dyes and their applications as far-red to NIR fluorescent probes for biomedical applications. In this review, we highlight the optical properties of representative flavylium dyes, design strategies, sensing mechanisms, and applications as fluorescent probes for detecting and visualizing important biomedical species and events. This review will prompt further research not only on flavylium dyes, but also into all far-red to NIR fluorophores and fluorescent probes. Moreover, this interest will hopefully spillover into applications related to complex biological systems and clinical treatments, ranging in focus from the sub-organelle to whole-animal levels.

Luminal Administration of a Water-soluble Carbon Monoxide-releasing Molecule (CORM-3) Mitigates Ischemia/Reperfusion Injury in Rats Following Intestinal Transplantation

BACKGROUND

The protective effects of carbon monoxide (CO) against ischemia/reperfusion (IR) injury during organ transplantation have been extensively investigated. Likewise, CO-releasing molecules (CORMs) are known to exert a variety of pharmacological activities via liberation of controlled amounts of CO in organs. Therefore, we hypothesized that intraluminal administration of water-soluble CORM-3 during cold storage of intestinal grafts would provide protective effects against IR injury.

METHODS

Orthotopic syngeneic intestinal transplantation was performed in Lewis rats following 6 h of cold preservation in Ringer solution or University of Wisconsin solution. Saline containing CORM-3 (100 µmol/L) or its inactive counterpart (iCORM-3) was intraluminally introduced in the intestinal graft before cold preservation.

RESULTS

Histopathological analysis of untreated and iCORM-3-treated grafts revealed a similar erosion and blunting of the intestinal villi. These changes in the mucosa structure were significantly attenuated by intraluminal administration of CORM-3. Intestinal mucosa damage caused by IR injury led to considerable deterioration of gut barrier function 3 h postreperfusion. CORM-3 significantly inhibited upregulation of proinflammatory mRNA levels, ameliorated intestinal morphological changes, and improved graft blood flow and mucosal barrier function. Additionally, CORM-3-treated grafts increased recipient survival rates. Pharmacological blockade of soluble guanylyl cyclase activity significantly reversed the protective effects conferred by CORM-3, indicating that CO partially mediates its therapeutic actions via soluble guanylyl cyclase activation.

CONCLUSIONS

Our study demonstrates that luminally delivered CORM-3 provides beneficial effects in cold-stored rat small intestinal grafts and could be an attractive therapeutic application of CO in the clinical setting of organ preservation and transplantation.

Modulatory Role of Carbon Monoxide on the Inflammatory Response and Oxidative Stress Linked to Gastrointestinal Disorders

Significance: Carbon monoxide (CO) is an endogenous gaseous mediator that plays an important role in maintaining gastrointestinal (GI) tract homeostasis, acting in mucosal defense, and providing negative modulation of pathophysiological markers of clinical conditions. Recent Advances: Preclinical studies using animal models and/or cell culture show that CO can modulate the inflammatory response and oxidative stress in GI mucosal injuries and pathological conditions, reducing proinflammatory cytokines and reactive oxygen species, while increasing antioxidant defense mechanisms. Critical Issues: CO has potent anti-inflammatory and antioxidant effects. The defense mechanisms of the GI tract are subject to aggression by different chemical agents (e.g., drugs and ethanol) as well as complex and multifactorial diseases, with inflammation and oxidative stress as strong triggers for the deleterious effects. Thus, it is possible that CO acts on a variety of molecules involved in the inflammatory and oxidative signaling cascades, as well as reinforcing several defense mechanisms that maintain GI homeostasis. Future Directions: CO-based therapies are promising tools for the treatment of GI disorders, such as gastric and intestinal injuries, inflammatory bowel disease, and pancreatitis. Therefore, it is necessary to develop safe and selective CO-releasing agents and/or donor drugs to facilitate effective treatments and methods for analysis of CO levels that are simple and inexpensive. Antioxid. Redox Signal. 37, 98-114.

Activatable Fluorescent-Photoacoustic Integrated Probes with Deep Tissue Penetration for Pathological Diagnosis and Therapeutic Evaluation of Acute Inflammation in Mice

Inflammation is associated with many diseases, so the development of an excellent near infrared fluorescent (NIRF) and photoacoustic (PA) dual-modality probe is crucial for the accurate diagnosis and efficacy evaluation of inflammation. However, most of the current NIRF/PA scaffolds are based on repurposing existing fluorescent dye platforms that exhibit non-optimal properties for both NIRF and PA signal outputs. Herein, we developed a novel dye scaffold QL-OH by optimizing the NIRF and PA signal of classical hemicyanine dyes. Based on this optimized dye, we developed the first NIRF/PA dual-mode carbon monoxide (CO) probe QL-CO for noninvasive and sensitive visualization of CO levels in deep inflammatory lesions in vivo. The novel probe QL-CO exhibited rapid and sensitive NIRF₇₇₅/PA₇₃₀ dual activation responses toward CO. In addition, the CO-activated probe QL-CO was successfully used for the diagnosis of inflammation and evaluation of anti-inflammation drug efficacy in living mice though the NIRF/PA dual-mode imaging technology for the first time. More importantly, the probe QL-CO could accurately locate the deep inflammatory lesion tissues (≈1 cm) in mice and obtain 3D PA diagnostic images with deep penetration depth and spatial resolution. Therefore, the new NIRF/PA dual-mode probe QL-CO has high potential for deep-tissue diagnosis imaging of CO in vivo. These findings may provide a new tool and approach for future research and diagnosis of CO-associated diseases.

CORM-2 prevents human gingival fibroblasts from lipoteichoic acid-induced VCAM-1 and ICAM-1 expression by inhibiting TLR2/MyD88/TRAF6/PI3K/Akt/ROS/NF-κB signaling pathway

Periodontal diseases are prevalent worldwide. Lipoteichoic acid (LTA), a major component of gram-positive bacteria, may play a key role in periodontally inflammatory diseases. Carbon monoxide (CO) is a critical messenger in many biological processes. It can elicit various biological properties, especially anti-inflammatory effects. As the straight administration of CO remains difficult, CO-releasing molecules (CO-RMs) are emerging as promising alternatives. To explore the pharmacological actions and signaling pathways of CO battling LTA-induced periodontal inflammation, this study investigated the cytoprotective effects of CORM-2 against the adhesion of THP-1 monocytes to human gingival fibroblasts (HGFs) and the underlying molecular mechanism. After exposing HGFs to LTA with or without CORM-2 pretreatment, monocyte adhesion was determined. VCAM-1 and ICAM-1 expression in HGFs was measured by real-time PCR. To identify the signaling pathways of CO involved in the cytoprotective effects of CORM-2, HGFs underwent pharmacological or genetical interventions before LTA incubation. The expression and/or activity of possible regulatory molecules were determined. The release of pro-inflammatory cytokines, including IL-1β, IL-6, and TNF-α, were measured using ELISA. The results showed that LTA increased cytokine production and upregulated VCAM-1 and ICAM-1 expression in HGFs, promoting monocyte adhesion. These events were dependent on TLR2/MyD88/TRAF6- and PI3K/Akt/NADPH oxidase/ROS-regulated NF-κB activation. CORM-2 inhibited LTA-induced inflammatory cascades in HGFs, in which CO seemed to be the hitman. To conclude, CO released from CORM-2 can prevent the LTA-stimulated HGFs from increasing VCAM-1 and ICAM-1 expression and promoting monocyte adhesion by inhibiting TLR2/MyD88/TRAF6 association and PI3K/Akt/NADPH oxidase/ROS signaling, both converge on the canonical NF-κB activation.

Energy-Efficient, On-Demand Activation of Biosensor Arrays for Long-Term Continuous Health Monitoring

Wearable biosensors for continuous health monitoring, particularly those used for glucose detection, have a limited operational lifetime due to biodegradation and fouling. As a result, patients must change sensors frequently, increasing cost and patient discomfort. Arrays of multiple sensors, where the individual devices can be activated on demand, increase overall operational longevity, thereby reducing cost and improving patient outcomes. This work demonstrates the feasibility of this approach via decomposition of combustible nitrocellulose membranes that protect the individual sensors from exposure to bioanalytes using a current pulse. Metal contacts, connected by graphene-loaded PEDOT:PSS polymer on the surface of the membrane, deliver the required energy to decompose the membrane. Nitrocellulose membranes with a thickness of less than 1 µm consistently transfer on to polydimethylsiloxane (PDMS) wells. An electrical energy as low as 68 mJ has been shown to suffice for membrane decomposition.

Downregulation of Vascular Hemeoxygenase-1 Leads to Vasculopathy in Systemic Sclerosis

Systemic sclerosis (SSc) is a terminal disease characterized by vasculopathy, tissue fibrosis, and autoimmunity. Although the exact etiology of SSc remains unknown, endothelial dysfunction, oxidative stress, and calcium handling dysregulation have been associated with a large number of SSc-related complications such as neointima formation, vasculogenesis, pulmonary arterial hypertension, impaired angiogenesis, and cardiac arrhythmias. Hemeoxygenase-1 (HO-1) is an antioxidant enzyme involved in multiple biological actions in the cardiovascular system including vascular tone, angiogenesis, cellular proliferation, apoptosis, and oxidative stress. The aim of this work was to investigate the physiological role of HO-1 and its relevance in the cardiovascular complications occurring in SSc. We found that, in early phases of SSc, the expression of HO-1 in dermal fibroblast is lower compared to those isolated from healthy control individuals. This is particularly relevant as reduction of the HO-1/CO signaling pathway is associated with endothelial dysfunction and vasculopathy. We show evidence of the role of HO-1/carbon monoxide (CO) signaling pathway in calcium handling. Using an in vitro model of pulmonary arterial hypertension (PAH) we investigated the role of HO-1 in Ca2+ mobilization from intracellular stores. Our results indicate that HO-1 regulates calcium release from intracellular stores of human pulmonary arterial endothelial cells. We interrogated the activity of HO-1 in angiogenesis using an organotypic co-culture of fibroblast-endothelial cell. Inhibition of HO-1 significantly reduced the ability of endothelial cells to form tubules. We further investigated if this could be associated with cell motility or migration of endothelial cells into the extracellular matrix synthesized by fibroblasts. By mean of holographic imaging, we studied the morphological and functional features of endothelial cells in the presence of an HO-1 activator and selective inhibitors. Our results demonstrate that inhibition of HO-1 significantly reduces cell proliferation and cell motility (migration) of cultured endothelial cells, whilst activation of HO-1 does not modify either morphology, proliferation or motility. In addition, we investigated the actions of CO on the Kv7.1 (KCQN1) channel current, an important component of the cardiac action potential repolarization. Using electrophysiology (whole-cell patch-clamp in a recombinant system overexpressing the KCQN1 channel), we assessed the regulation of KCQN1 by CO. CORM-2, a CO donor, significantly reduced the Kv7.1 current, suggesting that HO-1/CO signaling may play a role in the modulation of the cardiac action potential via regulation of this ion channel. In summary, our results indicate a clear link between: 1) downregulation of HO-1/CO signaling; and 2) pathophysiological processes occurring in early phases of SSc, such as calcium homeostasis dysregulation, impaired angiogenesis and cardiac arrhythmias. A better understanding of the canonical actions (mainly due to the biological actions of CO), and non-canonical actions of HO-1, as well as the interaction of HO-1/CO signaling with other gasotransmitters in SSc will contribute to the development of novel therapeutic approaches.

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.

Nanoformulation of a carbon monoxide releasing molecule protects against cyclosporin A-induced nephrotoxicity and renal fibrosis via the suppression of the NLRP3 inflammasome mediated TGF-β/Smad pathway

Cyclosporin A (CsA) induced nephrotoxicity i.e., renal fibrosis is a critical clinical problem in renal transplant patients, in which chronic inflammatory response is the major cause. Previously, we developed a nano-drug delivery system for carbon monoxide (CO), a multi-functional gaseous molecule with a potent anti-inflammatory effect, i.e., SMA/CORM2, which showed therapeutic potential in several inflammatory disease models. Accordingly, in this study, we explored the potential and usefulness of SMA/CORM2 on CsA induced renal fibrosis. When mice were exposed to CsA for 4 weeks, severe injuries in the kidney as revealed by decreased kidney function and histological examination, and activation of NLRP3 inflammasome, as well as renal fibrosis along with the upregulation of transforming growth factor β (TGFβ)/Smad signaling molecule were observed, whereas SMA/CORM2 (1 mg/kg) treatment remarkably ameliorated the inflammatory injury and fibrosis in the kidney. CO is the major effector molecule of SMA/CORM2 which significantly suppressed the activation of NLRP3 inflammasome, and induced the downregulation of TGFβ/Smad signaling. Inhibition of NLRP3 inflammasome by its inhibitor MCC950 also similarly decreased TGFβ/Smad expression and subsequently improved kidney injury and renal fibrosis, suggesting SMA/CORM2 induced suppression of TGFβ/Smad signaling and renal signaling via an NLRP3 inflammasome-dependent pathway. Compared to native CORM2, SMA/CORM2 exhibited better therapeutic/preventive effects owing to its superior water-solubility and bioavailability. These findings strongly indicated the applicability of SMA/CORM2 as an enhanced permeability and retention (EPR) effect-based nanomedicine for CsA induced renal fibrosis as well as other inflammatory diseases. STATEMENT OF SIGNIFICANCE: Carbon monoxide (CO) is an important gaseous signaling molecule that plays a crucial role in the maintenance of homeostasis. Because of its versatile functions, it exhibits the potential as the target molecule for many diseases, including inflammatory diseases and cancer. The development of stable and disease-targeted delivery systems of CO is thus of interest and importance. Previously we developed a nano micellar CO donor SMA/CORM2 which shows superior bioavailability and therapeutic potential in many inflammatory disease models. We reported here, SMA/CORM2, through controlled release of CO, greatly ameliorated CsA-induced renal fibrosis via suppressing the NLRP3 inflammasome mediated TGF-β/Smad pathway. These findings suggest a new anti-inflammatory mechanism of CO, which also provides a new approach for controlling CsA-induced nephrotoxicity.

CORM-401, an orally active carbon monoxide-releasing molecule, increases body temperature by activating non-shivering thermogenesis in rats

Thermoregulation is critical in health and disease and is tightly controlled to maintain body temperature homeostasis. Carbon monoxide (CO), an endogenous gasotransmitter produced during heme degradation by heme oxygenases, has been suggested to play a role in body core temperature (Tb) regulation. However, a direct involvement of CO in thermoregulation has not been confirmed and its mechanism(s) of action remain largely unknown. In the present study we characterized the effects of systemic delivery of CO by administration of an orally active CO-releasing molecule (CORM-401) on Tb regulation in conscious freely moving rats. Specifically, we evaluated the main thermo effectors in rats treated with CORM-401 by assessing: (i) non-shivering thermogenesis, i.e. the increased metabolism of brown fat measured through oxygen consumption and (ii) the rate of heat loss from the tail through calculations of heat loss index. We found that oral administration of CORM-401 (30 mg/kg) resulted in augmented CO delivery into the blood circulation as evidenced a by significant increase in carbon monoxy hemoglobin levels(COHb). In addition, treatment with CORM-401 increased Tb, which was caused by an elevated non-shivering thermogenesis indicated by increased oxygen consumption without significant changes in the tail heat loss. On the other hand, CORM-401 did not affect blood pressure, but significantly decreased heart rate. In summary, the findings of the present study reveal that increased circulating CO levels lead to a rise in Tb, which could have important implications in the emerging role of CO in the modulation of energetic metabolism.

Carbon monoxide and β-cell function: Implications for type 2 diabetes mellitus

Carbon monoxide (CO), a member of the multifunctional gasotransmitters family produced by heme oxygenases (i.e., HO-1 and HO-2), has received significant attention because of its involvement in carbohydrate metabolism. Experimental evidence indicates that both HO-2- and HO-1-derived CO stimulate insulin secretion, but the latter mainly acts as a compensatory response in pre-diabetes conditions. CO protects pancreatic β-cell against cytokine- and hypoxia-induced apoptosis and promotes β-cell regeneration. CO cross-talks with nitric oxide (NO) and hydrogen sulfide (H₂S), other important gasotransmitters in carbohydrate metabolism, in regulating β-cell function and insulin secretion. These data speak in favor of the potential therapeutic application of CO in type 2 diabetes mellitus (T2DM) and preventing the progression of pre-diabetes to diabetes. Either CO (as both gaseous form and CO-releasing molecule) or pharmacological formulations made of natural HO inducers (i.e., bioactive components originating from plant-based foods) are potential candidates for developing CO-based therapeutics in T2DM. Future studies are needed to assess the safety/efficacy and potential therapeutic applications of CO in T2DM.

Gases in Sepsis: Novel Mediators and Therapeutic Targets

Sepsis, a potentially lethal condition resulting from failure to control the initial infection, is associated with a dysregulated host defense response to pathogens and their toxins. Sepsis remains a leading cause of morbidity, mortality and disability worldwide. The pathophysiology of sepsis is very complicated and is not yet fully understood. Worse still, the development of effective therapeutic agents is still an unmet need and a great challenge. Gases, including nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H₂S), are small-molecule biological mediators that are endogenously produced, mainly by enzyme-catalyzed reactions. Accumulating evidence suggests that these gaseous mediators are widely involved in the pathophysiology of sepsis. Many sepsis-associated alterations, such as the elimination of invasive pathogens, the resolution of disorganized inflammation and the preservation of the function of multiple organs and systems, are shaped by them. Increasing attention has been paid to developing therapeutic approaches targeting these molecules for sepsis/septic shock, taking advantage of the multiple actions played by NO, CO and H₂S. Several preliminary studies have identified promising therapeutic strategies for gaseous-mediator-based treatments for sepsis. In this review article, we summarize the state-of-the-art knowledge on the pathophysiology of sepsis; the metabolism and physiological function of NO, CO and H₂S; the crosstalk among these gaseous mediators; and their crucial effects on the development and progression of sepsis. In addition, we also briefly discuss the prospect of developing therapeutic interventions targeting these gaseous mediators for sepsis.

Carbon Monoxide (CO), Nitric Oxide, and Hydrogen Sulfide Signaling During Acute CO Poisoning

Major toxic effects of acute carbon monoxide (CO) poisoning result from increases in reactive oxygen species (ROS) and reactive nitrogen species (RNS) producing oxidative stress. The importance of altered nitric oxide (NO) signaling in evoking increases in RNS during CO poisoning has been established. Although there is extensive literature describing NO and hydrogen sulfide (H2S) signaling in different types of cells under normal conditions, how CO poisoning-evoked deregulation of additional NO signaling pathways and H2S signaling pathways could result in cell injury has not been previously considered in detail. The goal of this article was to do this. The approach was to use published data to describe signaling pathways driven by CO bonding to different ferroproteins and then to collate data that describe NO and H2S signaling pathways that could interact with CO signaling pathways and be important during CO poisoning. Arteriolar smooth muscle cells—endothelial cells located in the coronary and some cerebral circulations—were used as a model to illustrate major signaling pathways driven by CO bonding to different ferroproteins. The results were consistent with the concept that multiple deregulated and interacting NO and H2S signaling pathways can be involved in producing cell injury evoked during acute CO poisoning and that these pathways interact with CO signaling pathways.

Heme Oxygenase-1: An Anti-Inflammatory Effector in Cardiovascular, Lung, and Related Metabolic Disorders

The heme oxygenase (HO) enzyme system catabolizes heme to carbon monoxide (CO), ferrous iron, and biliverdin-IXα (BV), which is reduced to bilirubin-IXα (BR) by biliverdin reductase (BVR). HO activity is represented by two distinct isozymes, the inducible form, HO-1, and a constitutive form, HO-2, encoded by distinct genes (HMOX1, HMOX2, respectively). HO-1 responds to transcriptional activation in response to a wide variety of chemical and physical stimuli, including its natural substrate heme, oxidants, and phytochemical antioxidants. The expression of HO-1 is regulated by NF-E2-related factor-2 and counter-regulated by Bach-1, in a heme-sensitive manner. Additionally, HMOX1 promoter polymorphisms have been associated with human disease. The induction of HO-1 can confer protection in inflammatory conditions through removal of heme, a pro-oxidant and potential catalyst of lipid peroxidation, whereas iron released from HO activity may trigger ferritin synthesis or ferroptosis. The production of heme-derived reaction products (i.e., BV, BR) may contribute to HO-dependent cytoprotection via antioxidant and immunomodulatory effects. Additionally, BVR and BR have newly recognized roles in lipid regulation. CO may alter mitochondrial function leading to modulation of downstream signaling pathways that culminate in anti-apoptotic, anti-inflammatory, anti-proliferative and immunomodulatory effects. This review will present evidence for beneficial effects of HO-1 and its reaction products in human diseases, including cardiovascular disease (CVD), metabolic conditions, including diabetes and obesity, as well as acute and chronic diseases of the liver, kidney, or lung. Strategies targeting the HO-1 pathway, including genetic or chemical modulation of HO-1 expression, or application of BR, CO gas, or CO donor compounds show therapeutic potential in inflammatory conditions, including organ ischemia/reperfusion injury. Evidence from human studies indicate that HO-1 expression may represent a biomarker of oxidative stress in various clinical conditions, while increases in serum BR levels have been correlated inversely to risk of CVD and metabolic disease. Ongoing human clinical trials investigate the potential of CO as a therapeutic in human disease.

Heme oxygenase-nitric oxide crosstalk-mediated iron homeostasis in plants under oxidative stress

Plant growth under abiotic stress conditions significantly enhances intracellular generation of reactive oxygen species (ROS). Oxidative status of plant cells is directly affected by the modulation of iron homeostasis. Among mammals and plants, heme oxygenase-1 (HO-1) is a well-known antioxidant enzyme. It catalyzes oxygenation of heme, thereby producing Fe²⁺, CO and biliverdin as byproducts. The antioxidant potential of HO-1 is primarily due to its catalytic reaction byproducts. Biliverdin and bilirubin possess conjugated π-electrons which escalate the ability of these biomolecules to scavenge free radicals. CO also enhances the ROS scavenging ability of plants cells by upregulating catalase and peroxidase activity. Enhanced expression of HO-1 in plants under oxidative stress accompanies sequestration of iron in specialized iron storage proteins localized in plastids and mitochondria, namely ferritin for Fe³⁺ storage and frataxin for storage of Fe-S clusters, respectively. Nitric oxide (NO) crosstalks with HO-1 at multiple levels, more so in plants under oxidative stress, in order to maintain intracellular iron status. Formation of dinitrosyl-iron complexes (DNICs) significantly prevents Fenton reaction during oxidative stress. DNICs also release NO upon dissociation in target cells over long distance in plants. They also function as antioxidants against superoxide anions and lipidic free radicals. A number of NO-modulated transcription factors also facilitate iron homeostasis in plant cells. Plants facing oxidative stress exhibit modulation of lateral root formation by HO-1 through NO and auxin-dependent pathways. The present review provides an in-depth analysis of the structure-function relationship of HO-1 in plants and mammals, correlating them with their adaptive mechanisms of survival under stress.

Flavonol-Based Carbon Monoxide Delivery Molecule with Endoplasmic Reticulum, Mitochondria, And Lysosome Localization

Light-triggered carbon monoxide (CO) delivery molecules are of significant current interest for evaluating the role of CO in biology and as potential therapeutics. Herein we report the first example of a metal free CO delivery molecule that can be tracked via confocal microscopy at low micromolar concentrations in cells prior to CO release. The NEt₂-appended extended flavonol (4) localizes to the endoplasmic reticulum, mitochondria, and lysosomes. Subcellular localization of 4 results in CO-induced toxicity effects that are distinct as compared to a nonlocalized analog. Anti-inflammatory effects of 4, as measured by TNF-α suppression, occur at the nanomolar level in the absence of CO release, and are enhanced with visible-light-induced CO release. Overall, the highly trackable nature of 4 enables studies of the biological effects of both a localized flavonol and CO release at low micromolar to nanomolar concentrations.

Regulation of protein function and degradation by heme, heme responsive motifs, and CO

Heme is an essential biomolecule and cofactor involved in a myriad of biological processes. In this review, we focus on how heme binding to heme regulatory motifs (HRMs), catalytic sites, and gas signaling molecules as well as how changes in the heme redox state regulate protein structure, function, and degradation. We also relate these heme-dependent changes to the affected metabolic processes. We center our discussion on two HRM-containing proteins: human heme oxygenase-2, a protein that binds and degrades heme (releasing Fe²⁺ and CO) in its catalytic core and binds Fe³⁺-heme at HRMs located within an unstructured region of the enzyme, and the transcriptional regulator Rev-erbβ, a protein that binds Fe³⁺-heme at an HRM and is involved in CO sensing. We will discuss these and other proteins as they relate to cellular heme composition, homeostasis, and trafficking. In addition, we will discuss the HRM-containing family of proteins and how the stability and activity of these proteins are regulated in a dependent manner through the HRMs. Then, after reviewing CO-mediated protein regulation of heme proteins, we turn our attention to the involvement of heme, HRMs, and CO in circadian rhythms. In sum, we stress the importance of understanding the various roles of heme and the distribution of the different heme pools as they relate to the heme redox state, CO, and heme binding affinities.

A water-soluble iron-porphyrin complex capable of rescuing CO-poisoned red blood cells

We describe herein a small-molecule platform that exhibits key properties needed by an antidote for CO poisoning. The design features an iron-porphyrin complex with bulky substituents above and below the...

Endocrine effects of three common gas signaling molecules in humans: A literature review

Gases such as hydrogen sulfide, nitric oxide and sulfur dioxide have important regulatory effects on the endocrine and physiological processes of the body and are collectively referred to as "gas signaling molecules". These gas signaling molecules are also closely related to Alzheimer's disease, the inflammatory response and depression. In this paper, we introduce the production and metabolic pathways of NO, H₂S and SO₂ in living organisms and review the regulatory functions of gas signaling molecules in the endocrine system and their mechanisms in relation to their clinical applications. This work will provide a basis for finding targets for intervention and establishing novel prevention and treatment strategies for related diseases.

: conjugation with a CO-releasing unit greatly enhances the anti-inflammatory activity of itaconates

Endogenous itaconate as well as the gasotransmitter CO have recently been described as powerful anti-inflammatory and immunomodulating agents. However, each of the two agents comes along with a major drawback: Whereas itaconates only exert beneficial effects at high concentrations above 100 μM, the uncontrolled application of CO has strong toxic effects. To solve these problems, we designed hybrid prodrugs, i.e. itaconates that are conjugated with an esterase-triggered CO-releasing acyloxycyclohexadiene-Fe(CO)₃ unit (ItaCORMs). Here, we describe the synthesis of different ItaCORMs and demonstrate their anti-inflammatory potency in cellular assays of primary murine immune cells in the low μmolar range (<10 μM). Thus, ItaCORMs represent a promising new class of hybrid compounds with high clinical potential as anti-inflammatory agents.