Carbon monoxide polyhemoglobin improves the therapeutic effect and relieves inflammation in the colon tissue of haemorrhagic shock/resuscitation rats.

OBJECTIVE: The objective of this study was to test the therapeutic effect of carbon monoxide polyhemoglobin (polyCOHb) in haemorrhagic shock/resuscitation and its underlying mechanisms. METHODS: 48 rats were divided into two experimental parts, and 36 rats in the first experiment and 12 rats in the second experiment. In the first experimental part, 36 animals were randomly assigned to the following groups: hydroxyethyl starch group (HES group, n = 12), polyhemoglobin group (polyHb group, n = 12), and carbon monoxide polyhemoglobin group (polyCOHb group, n = 12). In the second experimental part, 12 animals were randomly assigned to the following groups: polyHb group (n = 6), and polyCOHb group (n = 6). Then the anaesthetised rats were haemorrhaged by withdrawing 50% of the animal's blood volume (BV), and resuscitated to the same volume of the animal's withdrawing BV with HES, polyHb, polyCOHb. In the first experimental part, the 72h survival rates of each groups animals were measured. In the second experimental part, the rats' mean arterial pressure (MAP), heart rate (HR), blood gas levels and other indicators were dynamically monitored in baseline, haemorrhagic shock (HS), at 0point resuscitation (RS 0h) and after 1 h resuscitation (RS 1h). The concentrations of malondialdehyde (MDA), superoxide dismutase (SOD), tumour necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) were measured by ELISA kits in both groups of rats at RS 1h. Changes in pathological sections were examined by haematoxylin-eosin (HE) staining. Nuclear factor erythroid 2-related factor 2 (Nrf2) and haem oxygenase-1 (HO-1) levels were detected by immunohistochemical analysis, while myeloperoxidase (MPO) levels were detected by immunofluorescence. DHE staining was used to determine reactive oxygen species (ROS) levels. RESULTS: The 72h survival rates of the polyHb and polyCOHb groups were 50.00% (6/12) and 58.33% (7/12) respectively, which were significantly higher than that of the 8.33% (1/12) in the HES group (p < 0.05). At RS 0h and RS 1h, the HbCO content of rats in the polyCOHb group (1.90 ± 0.21, 0.80 ± 0.21) g/L were higher than those in the polyHb group (0.40 ± 0.09, 0.50 ± 0.12)g/L (p < 0.05); At RS 1h, the MDA (41.47 ± 3.89 vs 34.17 ± 3.87 nmol/ml) in the plasma, Nrf2 and HO-1 content in the colon of rats in the polyCOHb group were lower than the polyHb group. And the SOD in the plasma (605.01 ± 24.46 vs 678.64 ± 36.37) U/mg and colon (115.72 ± 21.17 vs 156.70 ± 21.34) U/mg and the MPO content in the colon in the polyCOHb group were higher than the polyHb group (p < 0.05). CONCLUSIONS: In these haemorrhagic shock/resuscitation models, both polyCOHb and polyHb show similar therapeutic effects, and polyCOHb has more effective effects in maintaining MAP, correcting acidosis, reducing inflammatory responses than that in polyHb.

Endogenous and exogeneous stimuli-triggered reactive oxygen species evoke long-lived carbon monoxide to fight against lung cancer.

Reactive oxygen species (ROS)-associated anticancer approaches usually suffer from two limitations, i.e., insufficient ROS level and short ROS half-life. Nevertheless, no report has synchronously addressed both concerns yet. Herein, a multichannel actions-enabled nanotherapeutic platform using hollow manganese dioxide (H-MnO2) carriers to load chlorin e6 (Ce6) sonosensitizer and CO donor (e.g., Mn2(CO)10) has been constructed to maximumly elevate ROS level and trigger cascade catalysis to produce CO. Therein, intratumoral H2O2 and ultrasound as endogenous and exogeneous triggers stimulate H-MnO2 and Ce6 to produce •OH and 1O2, respectively. The further cascade reaction between ROS and Mn2(CO)10 proceeds to release CO, converting short-lived ROS into long-lived CO. Contributed by them, such a maximumly-elevated ROS accumulation and long-lived CO release successfully suppresses the progression, recurrence and metastasis of lung cancer with a prolonged survival rate. More significantly, proteomic and genomic investigations uncover that the CO-induced activation of AKT signaling pathway, NRF-2 phosphorylation and HMOX-1 overexpression induce mitochondrial dysfunction to boost anti-tumor consequences. Thus, this cascade catalysis strategy can behave as a general means to enrich ROS and trigger CO release against refractory cancers.

Antimicrobial and anticancer properties of carbon monoxide releasing molecules of the fac-[Re(CO)3(N-N)L]+ family.

The toxicity profile of fac-[Re(CO)3(N-N)L]+ complexes against microbial and tumoral cells has been extensively studied, primarily focusing on modifications to the bidentate diimine (N-N) ligand. However, less attention has been paid to modifications of the axial ligand L, which is perpendicular to the Re-N-N plane. This study reveals that the high toxicity of the fac-[Re(CO)3(bpy)(Ctz)]+ complex may be attributed to the structural effect of the trityl (CPh3) group present in clotrimazole, as removal of phenyl rings causes a significant decrease in the activity against Staphylococcus aureus (S. aureus). Moreover, substitution of the 1-tritylimidazole ligand by the structurally related ligands PPh3 and PCy3 maintains similarly high activity levels. These findings contribute to understanding the interactions of toxic complexes with bacterial membranes, suggesting that the ligand structures play a crucial role in inhibiting cell wall synthesis processes, potentially including Lipid II synthesis. Compounds with Ph3E (E = C-imidazole; P) groups also showed to be 10 times more toxic than cisplatin against three mammalian cell lines (IC50: 2-4 µM). In contrast, the analogue 1-benzylimidazole and 1-tert-butylimidazole derivatives were as toxic as cisplatin. We observed that the decomposition of the [Re(I)(CO)3] fragment inside mammalian cell lines liberates CO, which is expected to exert biological effects. Therefore, compounds of this family possessing the structural motif Ph3E seem to combine high antimicrobial and antitumoral activities, the latter being much higher than that of cisplatin.

Carbon monoxide as a cellular protective agent in a swine model of cardiac arrest protocol.

Out-of-hospital cardiac arrest (OHCA) affects over 360,000 adults in the United States each year with a 50-80% mortality prior to reaching medical care. Despite aggressive supportive care and targeted temperature management (TTM), half of adults do not live to hospital discharge and nearly one-third of survivors have significant neurologic injury. The current treatment approach following cardiac arrest resuscitation consists primarily of supportive care and possible TTM. While these current treatments are commonly used, mortality remains high, and survivors often develop lasting neurologic and cardiac sequela well after resuscitation. Hence, there is a critical need for further therapeutic development of adjunctive therapies. While select therapeutics have been experimentally investigated, one promising agent that has shown benefit is CO. While CO has traditionally been thought of as a cellular poison, there is both experimental and clinical evidence that demonstrate benefit and safety in ischemia with lower doses related to improved cardiac/neurologic outcomes. While CO is well known for its poisonous effects, CO is a generated physiologically in cells through the breakdown of heme oxygenase (HO) enzymes and has potent antioxidant and anti-inflammatory activities. While CO has been studied in myocardial infarction itself, the role of CO in cardiac arrest and post-arrest care as a therapeutic is less defined. Currently, the standard of care for post-arrest patients consists primarily of supportive care and TTM. Despite current standard of care, the neurological prognosis following cardiac arrest and return of spontaneous circulation (ROSC) remains poor with patients often left with severe disability due to brain injury primarily affecting the cortex and hippocampus. Thus, investigations of novel therapies to mitigate post-arrest injury are clearly warranted. The primary objective of this proposed study is to combine our expertise in swine models of CO and cardiac arrest for future investigations on the cellular protective effects of low dose CO. We will combine our innovative multi-modal diagnostic platform to assess cerebral metabolism and changes in mitochondrial function in swine that undergo cardiac arrest with therapeutic application of CO.

Metal-based carbon monoxide releasing molecules with promising cytotoxic properties.

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

Dual delivery of carbon monoxide and doxorubicin using haemoglobin-albumin cluster: proof of concept for well-tolerated cancer therapy.

A serious concern of doxorubicin (DOX) therapy is that it causes severe adverse effects, particularly cardiotoxicity. Carbon monoxide (CO) possesses powerful cytoprotective effects against drug-induced organ injury and is expected to ameliorate DOX-induced cardiotoxicity. In this study, a dual carrier of DOX and CO (CO-HemoAct-DOX) was fabricated based on a haemoglobin-albumin cluster (HemoAct), which is a protein cluster with a haemoglobin core structure wrapped by serum albumin. CO-HemoAct-DOX was synthesised by binding CO to a haemoglobin core and covalently conjugating (6-maleimidocaproyl)hydrazone derivative of DOX to an albumin shell. The average DOX/cluster ratio was about 2.6. In the in vitro cytotoxicity assay against cancer cells, the anti-tumour activity of CO-HemoAct-DOX was 10-fold lower than that of DOX in a 2D-cultured model, whereas CO-HemoAct-DOX suppressed the growth of tumour spheroids to the same extent as DOX in the 3D-cultured model. In colon-26 tumour-bearing mice, CO-HemoAct-DOX achieved DOX delivery to the tumour site and alleviated tumour growth more effectively than DOX. Furthermore, CO-HemoAct attenuated DOX-induced cardiomyocyte atrophy in H9c2 cells and elevated the levels of cardiac biomarkers in mice exposed to DOX. These results suggest that the dual delivery of CO and DOX using HemoAct is a promising strategy as an anti-tumour agent to realise well-tolerated cancer therapy with minimal cardiotoxicity.

A CO-releasing coating based on carboxymethyl chitosan-functionalized graphene oxide for improving the anticorrosion and biocompatibility of magnesium alloy stent materials.

Due to its biofunctions similar to NO, the CO gas signaling molecule has gradually shown great potential in cardiovascular biomaterials for regulating the in vivo performances after the implantation and has received increasing attention. To construct a bioactive surface with CO-releasing properties on the surface of magnesium-based alloy to augment the anticorrosion and biocompatibility, graphene oxide (GO) was firstly modified using carboxymethyl chitosan (CS), and then CO-releasing molecules (CORM401) were introduced to synthesize a novel biocompatible nanomaterial (GOCS-CO) that can release CO in the physiological environments. The GOCS-CO was further immobilized on the magnesium alloy surface modified by polydopamine coating with Zn2+ (PDA/Zn) to create a bioactive surface capable of releasing CO in the physiological environment. The outcomes showed that the CO-releasing coating can not only significantly enhance the anticorrosion and abate the corrosion degradation rate of the magnesium alloy in a simulated physiological environment, but also endow it with good hydrophilicity and a certain ability to adsorb albumin selectively. Owing to the significant enhancement of anticorrosion and hydrophilicity, coupled with the bioactivity of GOCS, the modified sample not only showed excellent ability to prevent platelet adhesion and activation and reduce hemolysis rate but also can promote endothelial cell (EC) adhesion, proliferation as well as the expression of nitric oxide (NO) and vascular endothelial growth factor (VEGF). In the case of CO release, the hemocompatibility and EC growth behaviors were further significantly improved, suggesting that CO molecules released from the surface can significantly improve the hemocompatibility and EC growth. Consequently, the present study provides a novel surface modification method that can simultaneously augment the anticorrosion and biocompatibility of magnesium-based alloys, which will strongly promote the research and application of CO-releasing bioactive coatings for surface functionalization of cardiovascular biomaterials and devices.

Cascade Self-Generation of Carbon Monoxide Triggered by Photoinduced Holes for Efficient Hypoxic Tumors Therapy.

It still remains challenging to design multifunctional therapeutic reagents for effective cancer therapy under a unique tumor microenvironment including insufficient endogenous H2O2 and O2, low pH, and a high concentration of glutathione (GSH). In this work, a CO-based phototherapeutic system triggered by photogenerated holes, which consisted of ionic liquid (IL), the CO prodrug Mn2(CO)10, and iridium(III) porphyrin (IrPor) modified carbonized ZIF-8-doped graphitic carbon nitride nanocomposite (IL/ZCN@Ir(CO)), was designed for cascade hypoxic tumors. Upon light irradiation, the photogenerated holes on IL/ZCN@Ir(CO) oxidize water into H2O2, which subsequently induces Mn2(CO)10 to release CO. Meanwhile, IrPor can convert H2O2 to hydroxyl radical (•OH) and subsequent singlet oxygen (1O2), which further triggers CO release. Moreover, the degraded MnO2 shows activity for glutathione (GSH) depletion and mimics peroxidase, leading to GSH reduction and •OH production in tumors. Thus, this strategy can in situ release high concentrations of CO and reactive oxygen species (ROS) and deplete GSH to efficiently induce cell apoptosis under hypoxic conditions, which has a high inhibiting effect on the growth of tumors, offering an attractive strategy to amplify CO and ROS generation to meet therapeutic requirements in cancer treatment.

Carbon monoxide-induced autophagy enhances human mesenchymal stromal cell function via paracrine actions in murine polymicrobial sepsis.

Sepsis is a life-threatening process due to organ dysfunction resulting from severe infections. Mesenchymal stromal cells (MSCs) are being investigated as therapy for sepsis, along with conditioning regimens to improve their function. Carbon monoxide (CO) gas, which is cytoprotective at low doses, induces autophagy and is a mediator of inflammation. We evaluated CO-induced autophagy in human MSCs (hMSCs), and its impact on cell function in murine cecal ligation and puncture. Conditioning of hMSCs with CO ex vivo resulted in enhanced survival and bacterial clearance in vivo, and neutrophil phagocytosis of bacteria in vitro. Decreased neutrophil infiltration and less parenchymal cell death in organs were associated with increased macrophage efferocytosis of apoptotic neutrophils, promoting resolution of inflammation. These CO effects were lost when the cells were exposed to autophagy inhibition prior to gas exposure. When assessing paracrine actions of CO-induced autophagy, extracellular vesicles (EVs) were predominantly responsible. CO had no effect on EV production, but altered their miRNA cargo. Increased expression of miR-145-3p and miR-193a-3p by CO was blunted with disruption of autophagy, and inhibitors of these miRNAs led to a loss of neutrophil phagocytosis and macrophage efferocytosis. Collectively, CO-induced autophagy enhanced hMSC function during sepsis via paracrine actions of MSC-derived EVs.

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.

Cascade Reactions Catalyzed by Gold Hybrid Nanoparticles Generate CO Gas Against Periodontitis in Diabetes.

The treatment of diabetic periodontitis poses a significant challenge due to the presence of local inflammation characterized by excessive glucose concentration, bacterial infection, and high oxidative stress. Herein, mesoporous silica nanoparticles (MSN) are embellished with gold nanoparticles (Au NPs) and loaded with manganese carbonyl to prepare a carbon monoxide (CO) enhanced multienzyme cooperative hybrid nanoplatform (MSN-Au@CO). The Glucose-like oxidase activity of Au NPs catalyzes the oxidation of glucose to hydrogen peroxide (H2O2) and gluconic acid，and then converts H2O2 to hydroxyl radicals (•OH) by peroxidase-like activity to destroy bacteria. Moreover, CO production in response to H2O2, together with Au NPs exhibited a synergistic anti-inflammatory effect in macrophages challenged by lipopolysaccharides. The underlying mechanism can be the induction of nuclear factor erythroid 2-related factor 2 to reduce reactive oxygen species, and inhibition of nuclear factor kappa-B signaling to diminish inflammatory response. Importantly, the antibacterial and anti-inflammation effects of MSN-Au@CO are validated in diabetic rats with ligature-induced periodontitis by showing decreased periodontal bone loss with good biocompatibility. To summarize, MSN-Au@CO is fabricate to utilize glucose-activated cascade reaction to eliminate bacteria, and synergize with gas therapy to regulate the immune microenvironment, offering a potential direction for the treatment of diabetic periodontitis.

The carbon monoxide prodrug oCOm-21 increases Ca2+ sensitivity of the cardiac myofilament.

Patients undergoing cardiopulmonary bypass procedures require inotropic support to improve hemodynamic function and cardiac output. Current inotropes such as dobutamine, can promote arrhythmias, prompting a demand for improved inotropes with little effect on intracellular Ca2+ flux. Low-dose carbon monoxide (CO) induces inotropic effects in perfused hearts. Using the CO-releasing pro-drug, oCOm-21, we investigated if this inotropic effect results from an increase in myofilament Ca2+ sensitivity. Male Sprague Dawley rat left ventricular cardiomyocytes were permeabilized, and myofilament force was measured as a function of -log [Ca2+ ] (pCa) in the range of 9.0-4.5 under five conditions: vehicle, oCOm-21, the oCOm-21 control BP-21, and levosimendan, (9 cells/group). Ca2+ sensitivity was assessed by the Ca2+ concentration at which 50% of maximal force is produced (pCa50 ). oCOm-21, but not BP-21 significantly increased pCa50 compared to vehicle, respectively (pCa50 5.52 vs. 5.47 vs. 5.44; p < 0.05). No change in myofilament phosphorylation was seen after oCOm-21 treatment. Pretreatment of cardiomyocytes with the heme scavenger hemopexin, abolished the Ca2+ sensitizing effect of oCOm-21. These results support the hypothesis that oCOm-21-derived CO increases myofilament Ca2+ sensitivity through a heme-dependent mechanism but not by phosphorylation. Further analyses will confirm if this Ca2+ sensitizing effect occurs in an intact heart.

An oral carbon monoxide-releasing molecule protects against acute hyperhemolysis in sickle cell disease.

ABSTRACT: Acute hyperhemolysis is a severe life-threatening complication in patients with sickle cell disease (SCD) that may occur during delayed hemolytic transfusion reaction (DHTR), or vaso-occlusive crises associated with multiorgan failure. Here, we developed in vitro and in vivo animal models to mimic endothelial damage during the early phase of hyperhemolysis in SCD. We then used the carbon monoxide (CO)-releasing molecule CORM-401 and examined its effects against endothelial activation, damage, and inflammation inflicted by hemolysates containing red blood cell membrane-derived particles. The in vitro results revealed that CORM-401: (1) prevented the upregulation of relevant proinflammatory and proadhesion markers controlled by the NF-κB enhancer of activated B cells, and (2) abolished the expression of the nuclear factor erythroid-2-related factor 2 (Nrf2) that regulates the inducible antioxidant cell machinery. We also show in SCD mice that CORM-401 protects against hemolysate-induced acute damage of target organs such as the lung, liver, and kidney through modulation of NF-κB proinflammatory and Nrf2 antioxidant pathways. Our data demonstrate the efficacy of CORM-401 as a novel therapeutic agent to counteract hemolysate-induced organ damage during hyperhemolysis in SCD. This approach might be considered as possible preventive treatment in high-risk situations such as patients with SCD with history of DHTR.

On the Question of CO's Ability to Induce HO-1 Expression in Cell Culture: A Comparative Study Using Different CO Sources.

With the recognition of the endogenous signaling roles and pharmacological functions of carbon monoxide (CO), there is an increasing need to understand CO's mechanism of actions. Along this line, chemical donors have been introduced as CO surrogates for ease of delivery, dosage control, and sometimes the ability to target. Among all of the donors, two ruthenium-carbonyl complexes, CORM-2 and -3, are arguably the most commonly used tools for about 20 years in studying the mechanism of actions of CO. Largely based on data using these two CORMs, there has been a widely accepted inference that the upregulation of heme oxygenase-1 (HO-1) expression is one of the key mechanisms for CO's actions. However, recent years have seen reports of very pronounced chemical reactivities and CO-independent activities of these CORMs. We are interested in examining this question by conducting comparative studies using CO gas, CORM-2/-3, and organic CO donors in RAW264.7, HeLa, and HepG2 cell cultures. CORM-2 and CORM-3 treatment showed significant dose-dependent induction of HO-1 compared to "controls," while incubation for 6 h with 250-500 ppm CO gas did not increase the HO-1 protein expression and mRNA transcription level. A further increase of the CO concentration to 5% did not lead to HO-1 expression either. Additionally, we demonstrate that CORM-2/-3 releases minimal amounts of CO under the experimental conditions. These results indicate that the HO-1 induction effects of CORM-2/-3 are not attributable to CO. We also assessed two organic CO prodrugs, BW-CO-103 and BW-CO-111. BW-CO-111 but not BW-CO-103 dose-dependently increased HO-1 levels in RAW264.7 and HeLa cells. We subsequently studied the mechanism of induction with an Nrf2-luciferase reporter assay, showing that the HO-1 induction activity is likely due to the activation of Nrf2 by the CO donors. Overall, CO alone is unable to induce HO-1 or activate Nrf2 under various conditions in vitro. As such, there is no evidence to support attributing the HO-1 induction effect of the CO donors such as CORM-2/-3 and BW-CO-111 in cell culture to CO. This comparative study demonstrates the critical need to consider possible CO-independent effects of a chemical CO donor before attributing the observed biological effects to CO. It is also important to note that such in vitro results cannot be directly extrapolated to in vivo studies because of the increased level of complexity and the likelihood of secondary and/or synergistic effects in the latter.

Carbon monoxide is involved in melatonin-enhanced drought resistance in tomato seedlings by enhancing chlorophyll synthesis pathway.

BACKGROUND: Drought is thought to be a major abiotic stress that dramatically limits tomato growth and production. As signal molecule, melatonin (MT) and carbon monoxide (CO) can enhance plant stress resistance. However, the effect and underlying mechanism of CO involving MT-mediated drought resistance in seedling growth remains unknown. In this study, tomato (Solanum lycopersicum L. 'Micro-Tom') seedlings were used to investigate the interaction and mechanism of MT and CO in response to drought stress. RESULTS: The growth of tomato seedlings was inhibited significantly under drought stress. Exogenous MT or CO mitigated the drought-induced impairment in a dose-dependent manner, with the greatest efficiency provided by 100 and 500 µM, respectively. But application of hemoglobin (Hb, a CO scavenger) restrained the positive effects of MT on the growth of tomato seedlings under drought stress. MT and CO treatment promoted chlorophyll a (Chl a) and chlorophyll a (Chl b) accumulations. Under drought stress, the intermediate products of chlorophyll biosynthesis such as protoporphyrin IX (Proto IX), Mg-protoporphyrin IX (Mg-Proto IX), potochlorophyllide (Pchlide) and heme were increased by MT or CO, but uroporphyrinogen III (Uro III) content decreased in MT-treated or CO-treated tomato seedlings. Meanwhile, MT or CO up-regulated the expression of chlorophyll and heme synthetic-related genes SlUROD, SlPPOX, SlMGMT, SlFECH, SlPOR, SlChlS, and SlCAO. However, the effects of MT on chlorophyll biosynthesis were almost reversed by Hb. CONCLUSION: The results suggested that MT and CO can alleviate drought stress and facilitate the synthesis of Chl and heme in tomato seedlings. CO played an essential role in MT-enhanced drought resistance via facilitating chlorophyll biosynthesis pathway.

Membrane-Bound Redox Enzyme Cytochrome bd-I Promotes Carbon Monoxide-Resistant Escherichia coli Growth and Respiration.

The terminal oxidases of bacterial aerobic respiratory chains are redox-active electrogenic enzymes that catalyze the four-electron reduction of O2 to 2H2O taking out electrons from quinol or cytochrome c. Living bacteria often deal with carbon monoxide (CO) which can act as both a signaling molecule and a poison. Bacterial terminal oxidases contain hemes; therefore, they are potential targets for CO. However, our knowledge of this issue is limited and contradictory. Here, we investigated the effect of CO on the cell growth and aerobic respiration of three different Escherichia coli mutants, each expressing only one terminal quinol oxidase: cytochrome bd-I, cytochrome bd-II, or cytochrome bo3. We found that following the addition of CO to bd-I-only cells, a minimal effect on growth was observed, whereas the growth of both bd-II-only and bo3-only strains was severely impaired. Consistently, the degree of resistance of aerobic respiration of bd-I-only cells to CO is high, as opposed to high CO sensitivity displayed by bd-II-only and bo3-only cells consuming O2. Such a difference between the oxidases in sensitivity to CO was also observed with isolated membranes of the mutants. Accordingly, O2 consumption of wild-type cells showed relatively low CO sensitivity under conditions favoring the expression of a bd-type oxidase.

Red light-triggered release of ROS and carbon monoxide for combinational antibacterial application.

The abuse of antibiotics has led to the emergence of a wide range of drug-resistant bacteria. To address the challenge of drug-resistant bacterial infections and related infectious diseases, several effective antibacterial strategies have been developed. To achieve enhanced therapeutic effects, combinational treatment approaches should be employed. With this in mind, a metal-organic framework (MOF) based nanoreactor with integrated photodynamic therapy (PDT) and gas therapy which can release reactive oxygen species (ROS) and carbon monoxide (CO) under red light irradiation has been developed. The release of ROS and CO under red light irradiation exerts a preferential antibacterial effect on Gram-positive/Gram-negative bacteria. The bactericidal effects of ROS and CO on Staphylococcus aureus (S. aureus) and methicillin-resistant S. aureus (MRSA) are better than ROS only, showing a combinational antibacterial effect. Furthermore, the fluorescence emission properties of porphyrin moieties can be leveraged for real-time tracking and imaging of the nanoreactors. The simple preparation procedures of this material further enhance its potential as a versatile and effective antibacterial candidate, thereby presenting a new strategy for PDT and gas combinational treatment.

Hydrogels for Gasotransmitter Delivery: Nitric Oxide, Carbon Monoxide, and Hydrogen Sulfide.

Gasotransmitters, gaseous signaling molecules including nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2 S), maintain myriad physiological processes. Low levels of gasotransmitters are often associated with specific problems or diseases, so NO, CO, and H2 S hold potential in treating bacterial infections, chronic wounds, myocardial infarction, ischemia, and various other diseases. However, their clinical applications as therapeutic agents are limited due to their gaseous nature, short half-life, and broad physiological roles. One route toward the greater application of gasotransmitters in medicine is through localized delivery. Hydrogels are attractive biomedical materials for the controlled release of embedded therapeutics as they are typically biocompatible, possess high water content, have tunable mechanical properties, and are injectable in certain cases. Hydrogel-based gasotransmitter delivery systems began with NO, and hydrogels for CO and H2 S have appeared more recently. In this review, the biological importance of gasotransmitters is highlighted, and the fabrication of hydrogel materials is discussed, distinguishing between methods used to physically encapsulate small molecule gasotransmitter donor compounds or chemically tether them to a hydrogel scaffold. The release behavior and potential therapeutic applications of gasotransmitter-releasing hydrogels are also detailed. Finally, the authors envision the future of this field and describe challenges moving forward.

Recent progress on anti-nociceptive effects of carbon monoxide releasing molecule-2 (CORM-2).

The role of carbon monoxide (CO) has evolved albeit controversial disputes on its toxicity. This biological gasotransmitter participates in the endogenous regulation of neurotransmitters and neuropeptides released in the nervous system. Exogenous CO gas inhalation at a lower concentration has been the subject of investigations, which have revealed its biological homeostatic mechanisms and protective effects against many pathological conditions. This therapeutic procedure of CO is, however, limited due to its immediate release, which favours haemoglobin at a high affinity with the subsequent generation of toxic carboxyhaemoglobin in tissues. In order to address this problem, carbon monoxide releasing molecule-2 (CORM-2) or also known as tricarbonyldichlororuthenium II dimer is developed to liberate a controlled amount of CO in the biological systems. In this review, we examine several potential mechanisms exerted by this therapeutic compound to produce the anti-nociceptive effect that has been demonstrated in previous studies. This review could shed light on the role of CORM-2 to reduce pain, especially in cases of chronic and neuropathic pain.