Carbon monoxide-induced metabolic switch in adipocytes improves insulin resistance in obese mice

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 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.

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.

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.

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.

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.

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.

Delivery of therapeutic carbon monoxide by gas-entrapping materials

Carbon monoxide (CO) has long been considered a toxic gas but is now a recognized bioactive gasotransmitter with potent immunomodulatory effects. Although inhaled CO is currently under investigation for use in patients with lung disease, this mode of administration can present clinical challenges. The capacity to deliver CO directly and safely to the gastrointestinal (GI) tract could transform the management of diseases affecting the GI mucosa such as inflammatory bowel disease or radiation injury. To address this unmet need, inspired by molecular gastronomy techniques, we have developed a family of gas-entrapping materials (GEMs) for delivery of CO to the GI tract. We show highly tunable and potent delivery of CO, achieving clinically relevant CO concentrations in vivo in rodent and swine models. To support the potential range of applications of foam GEMs, we evaluated the system in three distinct disease models. We show that a GEM containing CO dose-dependently reduced acetaminophen-induced hepatocellular injury, dampened colitis-associated inflammation and oxidative tissue injury, and mitigated radiation-induced gut epithelial damage in rodents. Collectively, foam GEMs have potential paradigm-shifting implications for the safe therapeutic use of CO across a range of indications.

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.

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.

"CO in a pill": Towards oral delivery of carbon monoxide for therapeutic applications

Along with the impressive achievements in understanding the endogenous signaling roles and mechanism(s) of action of carbon monoxide (CO), much research has demonstrated the potential of using CO as a therapeutic agent for treating various diseases. Because of CO's toxicity at high concentrations and the observed difference in toxicity profiles of CO depending on the route of administration, this review analyzes and presents the benefits of developing orally active CO donors. Such compounds have the potential for improved safety profiles, enhancing the chance for developing CO-based therapeutics. In this review, the difference between inhalation and oral administration in terms of toxicity, CO delivery efficiency, and the potential mechanism(s) of action is analyzed. The evolution from CO gas inhalation to oral administration is also extensively analyzed by summarizing published studies up to date. The concept of "CO in a pill" can be achieved by oral administration of novel formulations of CO gas or appropriate CO donors.

Heme-oxygenase and lipid mediators in obesity and associated cardiometabolic diseases: Therapeutic implications

Obesity-mediated metabolic syndrome remains the leading cause of death worldwide. Among many potential targets for pharmacological intervention, a promising strategy involves the heme oxygenase (HO) system, specifically its inducible form, HO-1. This review collects and updates much of the current knowledge relevant to pharmacology and clinical medicine concerning HO-1 in metabolic diseases and its effect on lipid metabolism. HO-1 has pleotropic effects that collectively reduce inflammation, while increasing vasodilation and insulin and leptin sensitivity. Recent reports indicate that HO-1 with its antioxidants via the effect of bilirubin increases formation of biologically active lipid metabolites such as epoxyeicosatrienoic acid (EET), omega-3 and other polyunsaturated fatty acids (PUFAs). Similarly, HO-1and bilirubin are potential therapeutic targets in the treatment of fat-induced liver diseases. HO-1-mediated upregulation of EET is capable not only of reversing endothelial dysfunction and hypertension, but also of reversing cardiac remodeling, a hallmark of the metabolic syndrome. This process involves browning of white fat tissue (i.e. formation of healthy adipocytes) and reduced lipotoxicity, which otherwise will be toxic to the heart. More importantly, this review examines the activity of EET in biological systems and a series of pathways that explain its mechanism of action and discusses how these might be exploited for potential therapeutic use. We also discuss the link between cardiac ectopic fat deposition and cardiac function in humans, which is similar to that described in obese mice and is regulated by HO-1-EET-PGC1α signaling, a potent negative regulator of the inflammatory adipokine NOV.

Adipose tissue senescence is mediated by increased ATP content after a short-term high-fat diet exposure

In the context of obesity, senescent cells accumulate in white adipose tissue (WAT). The cellular underpinnings of WAT senescence leading to insulin resistance are not fully elucidated. The objective of the current study was to evaluate the presence of WAT senescence early after initiation of high‐fat diet (HFD, 1–10 weeks) in 5‐month‐old male C57BL/6J mice and the potential role of energy metabolism. We first showed that WAT senescence occurred 2 weeks after HFD as evidenced in whole WAT by increased senescence‐associated ß‐galactosidase activity and cyclin‐dependent kinase inhibitor 1A and 2A expression. WAT senescence affected various WAT cell populations, including preadipocytes, adipose tissue progenitors, and immune cells, together with adipocytes. WAT senescence was associated with higher glycolytic and mitochondrial activity leading to enhanced ATP content in HFD‐derived preadipocytes, as compared with chow diet‐derived preadipocytes. One‐month daily exercise, introduced 5 weeks after HFD, was an effective senostatic strategy, since it reversed WAT cellular senescence, while reducing glycolysis and production of ATP. Interestingly, the beneficial effect of exercise was independent of body weight and fat mass loss. We demonstrated that WAT cellular senescence is one of the earliest events occurring after HFD initiation and is intimately linked to the metabolic state of the cells. Our data uncover a critical role for HFD‐induced elevated ATP as a local danger signal inducing WAT senescence. Exercise exerts beneficial effects on adipose tissue bioenergetics in obesity, reversing cellular senescence, and metabolic abnormalities.

Increased Sirt1 secreted from visceral white adipose tissue is associated with improved glucose tolerance in obese Nrf2-deficient mice

Obesity is associated with metabolic dysregulation characterized by insulin resistance and glucose intolerance. Nuclear factor E2-related factor (Nrf2) is a critical regulator of the stress response and Nrf2-deficient mice (Nrf2-/-) are protected against high fat diet (HFD)-induced metabolic derangement. We searched for factors that could underline this favorable phenotype and found that Nrf2-/- mice exhibit higher circulating levels of sirtuin 1 (Sirt1), a key player in cellular homeostasis and energy metabolism, compared to wild-type mice. Increased Sirt1 levels in Nrf2-/- mice were found not only in animals under standard diet but also following HFD. Interestingly, we report here that the visceral adipose tissue (eWAT) is the sole source of increased Sirt1 protein in plasma. eWAT and other fat depots displayed enhanced adipocytes lipolysis, increased fatty acid oxidation and glycolysis, suggesting autocrine and endocrine actions of Sirt1 in this model. We further demonstrate that removal of eWAT completely abolishes the increase in circulating Sirt1 and that this procedure suppresses the beneficial effect of Nrf2 deficiency on glucose tolerance, but not insulin sensitivity, following a HFD regime. Thus, in contrast to many other stressful conditions where Nrf2 deficiency exacerbates damage, our study indicates that up-regulation of Sirt1 levels specifically in the visceral adipose tissue of Nrf2-/- mice is a key adaptive mechanism that mitigates glucose intolerance induced by nutritional stress.

Gasotransmitter signaling in energy homeostasis and metabolic disorders

Gasotransmitters are small molecules of gases, including nitric oxide (NO), hydrogen sulfide (H₂S), and carbon monoxide (CO). These three gasotransmitters can be endogenously produced and regulate a wide range of pathophysiological processes by interacting with specific targets upon diffusion in the biological media. By redox and epigenetic regulation of various physiological functions, NO, H₂S, and CO are critical for the maintenance of intracellular energy homeostasis. Accumulated evidence has shown that these three gasotransmitters control ATP generation, mitochondrial biogenesis, glucose metabolism, insulin sensitivity, lipid metabolism, and thermogenesis, etc. Abnormal generation and metabolism of NO, H₂S, and/or CO are involved in various abnormal metabolic diseases, including obesity, diabetes, and dyslipidemia. In this review, we summarized the roles of NO, H₂S, and CO in the regulation of energy homeostasis as well as their involvements in the metabolism of dysfunction-related diseases. Understanding the interaction among these gasotransmitters and their specific molecular targets are very important for therapeutic applications.

Pharmacological modulation of the hydrogen sulfide (H2 S) system by dietary H2 S-donors: A novel promising strategy in the prevention and treatment of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) represents the most common age-related metabolic disorder, and its management is becoming both a health and economic issue worldwide. Moreover, chronic hyperglycemia represents one of the main risk factors for cardiovascular complications. In the last years, the emerging evidence about the role of the endogenous gasotransmitter hydrogen sulfide (H₂ S) in the pathogenesis and progression of T2DM led to increasing interest in the pharmacological modulation of endogenous "H₂ S-system". Indeed, H₂ S directly contributes to the homeostatic maintenance of blood glucose levels; moreover, it improves impaired angiogenesis and endothelial dysfunction under hyperglycemic conditions. Moreover, H₂ S promotes significant antioxidant, anti-inflammatory, and antiapoptotic effects, thus preventing hyperglycemia-induced vascular damage, diabetic nephropathy, and cardiomyopathy. Therefore, H₂ S-releasing molecules represent a promising strategy in both clinical management of T2DM and prevention of macro- and micro-vascular complications associated to hyperglycemia. Recently, growing attention has been focused on dietary organosulfur compounds. Among them, garlic polysulfides and isothiocyanates deriving from Brassicaceae have been recognized as H₂ S-donors of great pharmacological and nutraceutical interest. Therefore, a better understanding of the therapeutic potential of naturally occurring H₂ S-donors may pave the way to a more rational use of these nutraceuticals in the modulation of H₂ S homeostasis in T2DM.

Heme Oxygenase 1 and 2 Differentially Regulate Glucose Metabolism and Adipose Tissue Mitochondrial Respiration: Implications for Metabolic Dysregulation

Heme oxygenase (HO) consists of inducible (HO-1) and constitutive (HO-2) isoforms that are encoded by Hmox1 and Hmox2 genes, respectively. As an anti-inflammatory and antioxidant molecule, HO participates in the development of metabolic diseases. Whether Hmox deficiency causes metabolic abnormalities under basal conditions remains unclear. We hypothesized that HO-1 and HO-2 differentially affect global and adipose tissue metabolism. To test this hypothesis, we determined insulin sensitivity, glucose tolerance, energy expenditure, and respiratory exchange ratio in global Hmox1^-/- and Hmox2^-/- mice. Body weight was reduced in female but not male Hmox1^-/- and Hmox2^-/- mice. Reduced insulin sensitivity and physical activity were observed in Hmox1^-/- but not Hmox2^-/- mice. Deletion of either Hmox1 or Hmox2 had no effects on glucose tolerance, energy expenditure or respiratory exchange ratio. Mitochondrial respiration was unchanged in gonadal fat pads (white adipose tissue, WAT) of Hmox1^-/- mice. Hmox2 deletion increased proton leak and glycolysis in gonadal, but not interscapular fat tissues (brown adipose tissue, BAT). Uncoupling protein and Hmox1 genes were unchanged in gonadal fat pads of Hmox2^-/- mice. Conclusively, HO-1 maintains insulin sensitivity, while HO-2 represses glycolysis and proton leak in the WAT under basal condition. This suggests that HO-1 and HO-2 differentially modulate metabolism, which may impact the metabolic syndrome.

Progesterone receptor membrane associated component 1 enhances obesity progression in mice by facilitating lipid accumulation in adipocytes

Progesterone receptor membrane associated component 1 (PGRMC1) exhibits haem-dependent dimerization on cell membrane and binds to EGF receptor and cytochromes P450 to regulate cancer proliferation and chemoresistance. However, its physiological functions remain unknown. Herein, we demonstrate that PGRMC1 is required for adipogenesis, and its expression is significantly enhanced by insulin or thiazolidine, an agonist for PPARγ. The haem-dimerized PGRMC1 interacts with low-density lipoprotein receptors (VLDL-R and LDL-R) or GLUT4 to regulate their translocation to the plasma membrane, facilitating lipid uptake and accumulation, and de-novo fatty acid synthesis in adipocytes. These events are cancelled by CO through interfering with PGRMC1 dimerization. PGRMC1 expression in mouse adipose tissues is enhanced during obesity induced by a high fat diet. Furthermore, adipose tissue-specific PGRMC1 knockout in mice dramatically suppressed high-fat-diet induced adipocyte hypertrophy. Our results indicate a pivotal role of PGRMC1 in developing obesity through its metabolic regulation of lipids and carbohydrates in adipocytes.

Skeletal muscle mitochondrial fragmentation and impaired bioenergetics from nutrient overload are prevented by carbon monoxide

Nutrient excess increases skeletal muscle oxidant production and mitochondrial fragmentation that may result in impaired mitochondrial function, a hallmark of skeletal muscle insulin resistance. This led us to explore whether an endogenous gas molecule, carbon monoxide (CO), which is thought to prevent weight gain and metabolic dysfunction in mice consuming high-fat diets, alters mitochondrial morphology and respiration in C2C12 myoblasts exposed to high glucose (15.6 mM) and high fat (250 µM BSA-palmitate) (HGHF). Also, skeletal muscle mitochondrial morphology, distribution, respiration, and energy expenditure were examined in obese resistant (OR) and obese prone (OP) rats that consumed a high-fat and high-sucrose diet for 10 wk with or without intermittent low-dose inhaled CO and/or exercise training. In cells exposed to HGHF, superoxide production, mitochondrial membrane potential (ΔΨm), mitochondrial fission regulatory protein dynamin-related protein 1 (Drp1) and mitochondrial fragmentation increased, while mitochondrial respiratory capacity was reduced. CO decreased HGHF-induced superoxide production, Drp1 protein levels and mitochondrial fragmentation, maintained ΔΨm, and increased mitochondrial respiratory capacity. In comparison with lean OR rats, OP rats had smaller skeletal muscle mitochondria that contained disorganized cristae, a normal mitochondrial distribution, but reduced citrate synthase protein expression, normal respiratory responses, and a lower energy expenditure. The combination of inhaled CO and exercise produced the greatest effect on mitochondrial morphology, increasing ADP-stimulated respiration in the presence of pyruvate, and preventing a decline in resting energy expenditure. These data support a therapeutic role for CO and exercise in preserving mitochondrial morphology and respiration during metabolic overload.

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

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

Heme Oxygenase-1 Upregulation: A Novel Approach in the Treatment of Cardiovascular Disease

Significance: Heme oxygenase (HO) plays a pivotal role in both vascular and metabolic functions and is involved in many physiological and pathophysiological processes in vascular endothelial cells (ECs) and adipocytes. Recent Advances: From the regulation of adipogenesis in adipose tissue to the adaptive response of vascular tissue in the ECs, HO plays a critical role in the capability of the vascular system to respond and adjust to insults in homeostasis. Recent studies show that HO-1 through regulation of adipocyte and adipose tissue functions ultimately aid not only in local but also in systemic maintenance of homeostasis. Critical Issues: Recent advances have revealed the existence of a cross talk between vascular ECs and adipocytes in adipose tissue. In the pathological state of obesity, this cross talk contributes to the condition's adverse chronic effects, and we propose that specific targeting of the HO-1 gene can restore signaling pathways and improve both vascular and adipose functions. Future Directions: A complete understanding of the role of HO-1 in regulation of cardiovascular homeostasis is important to comprehend the homeostatic regulation as well as in cardiovascular disease. Efforts are required to highlight the effects and the ability to target the HO-1 gene in models of obesity with an emphasis on the role of pericardial fat on cardiovascular health.

Carbon Monoxide and Exercise Prevents Diet-Induced Obesity and Metabolic Dysregulation Without Affecting Bone

OBJECTIVE

Carbon monoxide (CO) may counteract obesity and metabolic dysfunction in rodents consuming high-fat diets, but the skeletal effects are not understood. This study investigated whether low-dose inhaled CO (250 ppm) with or without moderate intensity aerobic exercise (3 h/wk) would limit diet-induced obesity and metabolic dysregulation and preserve bone health.

METHODS

Obesity-resistant (OR) rats served as controls, and obesity-prone (OP) rats were randomized to sedentary, sedentary plus CO, exercise, or CO plus exercise. For 10 weeks, OP rats consumed a high-fat, high-sucrose diet, whereas OR rats consumed a low-fat control diet. Measurements included indicators of obesity and metabolism, bone turnover markers, femoral geometry and microarchitecture, bone mechanical properties, and tibial morphometry.

RESULTS

A high-fat, high-sucrose diet led to obesity, hyperinsulinemia, and hyperleptinemia, without impacting bone. CO alone led only to a modest reduction in weight gain. Exercise attenuated weight gain and improved the metabolic profile; however, bone fragility increased. Combined CO and exercise led to body mass reduction and a metabolic state similar to control OR rats and prevented the exercise-induced increase in bone fragility.

CONCLUSIONS

CO and aerobic exercise training prevent obesity and metabolic sequelae of nutrient excess while stabilizing bone physiology.

CO-mediated cytoprotection is dependent on cell metabolism modulation

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

Effects of frequently applied carbon monoxide releasing molecules (CORMs) in typical CO-sensitive model systems - A comparative in vitro study

Intracellular carbon monoxide (CO) is a gaseous signaling molecule and is generated enzymatically by heme oxygenases upon degradation of heme to billiverdin. Target structures for intracellular produced CO are heme proteins including cytochrome c oxidase of the respiratory chain, cytochrome P450-dependent monooxygenases, or myoglobin. For studies on CO signaling, CO-releasing molecules (CORMs) of different structure are available. Here, three frequently used CORMs (CORM-2, CORM-3 and CORM-401) were studied for their properties to provide CO in biological test systems and address susceptible heme proteins. CO release was investigated in the myoglobin binding assay and found to be rapid (<5 min) with CORM-2- and CORM-3, whereas CORM-401 continuously provided CO (>50 min). Storage stability of CORM stock solutions was also assessed with the myoglobin assay. Only CORM-401 stock solutions were stable over a period of 7 days. Incubation of CORMs with recombinant cytochrome P450 led to an inhibition of enzyme activity. However, only CORM-3 and CORM-401 proved to be suitable in this test system because controls with the inactivated CORM-2 (iCORM-2) also led to a loss of enzyme activity. The impact of CORMs on the respiratory chain was investigated with high resolution respirometry and extracellular flux technology. In the first approach interferences of CORM-2 and CORM-3 with oxygen measurement occurred, since a rapid depletion of oxygen was detected in the medium even when no cells were present. However, CORM-401 did not interfere with oxygen measurement and the expected inhibition of cellular respiration was observed. CORM-2 was not suitable for use in oxygen measurements with the extracellular flux technology and CORM-3 application did not show any effect in this system. However, CO-dependent inhibition of cellular respiration was observed with CORM-401. Based on the present experiments it is concluded, that CORM-401 produced most reliable CO-specific results for the modulation of typical CO targets. For studies on CO-dependent biological effects on intracellular heme groups, CORM-2 and CORM-3 were less suitable. Depending on the experimental setting, data achieved with these compounds should be evaluated with caution.

Therapeutic effects of CO-releaser/Nrf2 activator hybrids (HYCOs) in the treatment of skin wound, psoriasis and multiple sclerosis

Carbon monoxide (CO) produced by heme oxygenase-1 (HO-1) or delivered by CO-releasing molecules (CO-RMs) exerts anti-inflammatory action, a feature also exhibited by the nuclear factor erythroid 2-related factor 2 (Nrf2), a master regulator of the stress response. We have recently developed new hybrid molecules (HYCOs) consisting of CO-RMs conjugated to fumaric esters known to activate Nrf2/HO-1. Here we evaluated the biological activities of manganese (Mn) and ruthenium (Ru)-based HYCOs in human monocytes and keratinocytes in vitro as well as in vivo models of inflammation. The effects of HYCOs were compared to: a) dimethyl fumarate (DMF), a known fumaric ester used in the clinic; b) a CO-RM alone; or c) the combination of the two compounds. Mn–HYCOs donated CO and up-regulated Nrf2/HO-1 in vitro more efficiently than Ru–HYCOs. However, irrespective of the metal, a strong reduction in anti-inflammatory markers in monocytes stimulated by LPS was observed with specific HYCOs. This effect was not observed with DMF, CO-RM alone or the combination of the two, indicating the enhanced potency of HYCOs compared to the separate entities. Selected HYCOs given orally to mice accelerated skin wound closure, reduced psoriasis-mediated inflammation and disease symptoms equalling or surpassing the effect of DMF, and ameliorated motor dysfunction in a mouse model of multiple sclerosis. Thus, HYCOs have potent anti-inflammatory activities that are recapitulated in disease models in which inflammation is a prominent component. Prolonged daily administration of HYCOs (up to 40 days) is well tolerated in animals. Our results clearly confirm that HYCOs possess a dual mode of action highlighting the notion that simultaneous Nrf2 targeting and CO delivery could be a clinically relevant application to combat inflammation.

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HYCOs are dual activity molecules targeting the Nrf2/HO-1 axis and delivering carbon monoxide.

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Mn- and Ru-based HYCOs were compared in in vitro and in vivo models of inflammation.

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HYCOs reduce inflammation in monocytes and increase proliferation in keratinocytes.

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Oral administration of HYCOs accelerates skin wound healing and ameliorates psoriasis and multiple sclerosis.

Role of Heme Oxygenase as a Modulator of Heme-Mediated Pathways

The heme oxygenase (HO) system is essential for heme and iron homeostasis and necessary for adaptation to cell stress. HO degrades heme to biliverdin (BV), carbon monoxide (CO) and ferrous iron. Although mostly beneficial, the HO reaction can also produce deleterious effects, predominantly attributed to excessive product formation. Underrated so far is, however, that HO may exert effects additionally via modulation of the cellular heme levels. Heme, besides being an often-quoted generator of oxidative stress, plays also an important role as a signaling molecule. Heme controls the anti-oxidative defense, circadian rhythms, activity of ion channels, glucose utilization, erythropoiesis, and macrophage function. This broad spectrum of effects depends on its interaction with proteins ranging from transcription factors to enzymes. In degrading heme, HO has the potential to exert effects also via modulation of heme-mediated pathways. In this review, we will discuss the multitude of pathways regulated by heme to enlarge the view on HO and its role in cell physiology. We will further highlight the contribution of HO to pathophysiology, which results from a dysregulated balance between heme and the degradation products formed by HO.

Cardioprotective Heme Oxygenase-1-PGC1α Signaling in Epicardial Fat Attenuates Cardiovascular Risk in Humans as in Obese Mice

OBJECTIVE

This study investigated whether levels of signaling pathways and inflammatory adipokines in epicardial fat regulate cardiovascular risks in humans and mice.

METHODS

Epicardial fat was obtained from the hearts of patients with heart failure requiring coronary artery bypass surgery, and signaling pathways were compared with visceral fat. The genetic profile of epicardial and visceral fat from humans was also compared with genetic profiles of epicardial and visceral fat in obese mice. Left ventricular (LV) fractional shortening was measured in obese mice before and after treatment with inducers of mitochondrial signaling heme oxygenase 1 (HO-1)-peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α). An RNA array/heat map on 88 genes that regulate adipose tissue function was used to identify a target gene network.

RESULTS

Human epicardial fat gene profiling showed decreased levels of mitochondrial signaling of HO-1-PGC1α and increased levels of the inflammatory adipokine CCN family member 3. Similar observations were seen in epicardial and visceral fat of obese mice. Improvement in LV function was linked to the increase in mitochondrial signaling in epicardial fat of obese mice.

CONCLUSIONS

There is a link between cardiac ectopic fat deposition and cardiac function in humans that is similar to that which is described in obese mice. An increase of mitochondrial signaling pathway gene expression in epicardial fat attenuates cardiometabolic dysfunction and LV fractional shortening in obese mice.

Carbon monoxide releasing molecule-A1 improves nonalcoholic steatohepatitis via Nrf2 activation mediated improvement in oxidative stress and mitochondrial function

Nuclear factor-erythroid 2 related factor 2 (Nrf2)-mediated signaling plays a central role in maintaining cellular redox homeostasis of hepatic cells. Carbon monoxide releasing molecule-A1 (CORM-A1) has been reported to stimulate up-regulation and nuclear translocation of Nrf2 in hepatocytes. However, the role of CORM-A1 in improving lipid metabolism, antioxidant signaling and mitochondrial functions in nonalcoholic steatohepatitis (NASH) is unknown. In this study, we report that CORM-A1 prevents hepatic steatosis in high fat high fructose (HFHF) diet fed C57BL/6J mice, used as model of NASH. The beneficial effects of CORM-A1 in HFHF fed mice was associated with improved lipid homeostasis, Nrf2 activation, upregulation of antioxidant responsive (ARE) genes and increased ATP production. As, mitochondria are intracellular source of reactive oxygen species (ROS) and important sites of lipid metabolism, we further investigated the mechanisms of action of CORM-A1-mediated improvement in mitochondrial function in palmitic acid (PA) treated HepG2 cells. Cellular oxidative stress and cell viability were found to be improved in PA + CORM-A1 treated cells via Nrf2 translocation and activation of cytoprotective genes. Furthermore, in PA treated cells, CORM-A1 improved mitochondrial oxidative stress, membrane potential and rescued mitochondrial biogenesis thru upregulation of Drp1, TFAM, PGC-1α and NRF-1 genes. CORM-A1 treatment improved cellular status by lowering glycolytic respiration and maximizing OCR. Improvement in mitochondrial respiration and increment in ATP production in PA + CORM-A1 treated cells further corroborate our findings. In summary, our data demonstrate for the first time that CORM-A1 ameliorates tissue damage in steatotic liver via Nrf2 activation and improved mitochondrial function, thus, suggesting the anti-NASH potential of CORM-A1.

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CORM-A1 facilitates Nrf2 translocation and regulates cellular redox homeostasis in liver.

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CORM-A1 improves antioxidant status and lipid metabolism in liver.

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CORM-A1 induces mitochondrial biogenesis, improves energetics and cellular respiration in HepG2 cells.

Design and Biological Evaluation of Manganese- and Ruthenium-Based Hybrid CO-RMs (HYCOs)

Interest in the therapeutic effects of carbon monoxide (CO), a product of heme degradation catalyzed by the enzyme heme oxygenase-1 (HO-1), has led to the development of CO-releasing molecules (CO-RMs) for the controlled delivery of this gas in vivo. We recently proposed conjugating a cobalt-based CO-RM with various activators of nuclear factor erythroid 2-related factor 2 (Nrf2), the transcription factor that regulates HO-1 expression, in order to exploit the beneficial effects of exogenous and endogenous CO. In this study, we describe the preparation of hybrid molecules (termed HYCOs) conjugating a fumaric acid derivative as an Nrf2 activator to a Mn- or a Ru-based CO-RM known to be pharmacologically active. With the exception of an acyl-manganese complex, these hybrids were obtained by associating the two bioactive entities by means of a linker of variable structure. X-ray diffraction analyses and preliminary biological investigations are also presented.

HO-1 overexpression and underexpression: Clinical implications

In this review we examine the effects of both over- and under-production of heme oxygenase-1 (HO-1) and HO activity on a broad spectrum of biological systems and on vascular disease. In a few instances e.g., neonatal jaundice, overproduction of HO-1 and increased HO activity results in elevated levels of bilirubin requiring clinical intervention with inhibitors of HO activity. In contrast HO-1 levels and HO activity are low in obesity and the HO system responds to mitigate the deleterious effects of oxidative stress through increased levels of bilirubin (anti-inflammatory) and CO (anti-apoptotic) and decreased levels of heme (pro-oxidant). Site specific HO-1 overexpression diminishes adipocyte terminal differentiation and lipid accumulation of obesity mediated release of inflammatory molecules. A series of diverse strategies have been implemented that focus on increasing HO-1 and HO activity that are central to reversing the clinical complications associated with diseases including, obesity, metabolic syndrome and vascular disease.

Positive Effects of Heme Oxygenase Upregulation on Adiposity and Vascular Dysfunction: Gene Targeting vs. Pharmacologic Therapy

Objective: Heme oxygenase (HO-1) plays a critical role in adipogenesis and it is important to understand its function in obesity. Many studies have shown that upregulation of HO-1 can affect the biologic parameters in obesity-mediated diabetes, hypertension and vascular endothelial cell function. Thus, we aimed to explore the hypothesis that upregulation of HO-1, using a pharmacologic approach as well as gene targeting, would improve both adiposity and endothelial cell dysfunction by direct targeting of endothelial cells. Our second aim was to compare the short-term effect of a HO-1 inducer, cobalt-protoporphrin IX (CoPP), with the long-term effects of gene targeted therapy on vascular and adipocyte stem cells in obese mice. Method: We examined the effect of CoPP on fat pre-adipocytes and mesenchymal stem cells (MSC) in mice fed a high-fat diet (HFD). We also used a lentiviral construct that expressed heme oxygenase (HO-1) that was under the control of an endothelium specific promoter, vascular endothelium cadherin (VECAD) heme oxygenase (VECAD-HO-1). We targeted endothelial cells using vascular endothelium cadherin/green fluorescent protein fusion construct (VECAD-GFP) as the control. Conditioned media (CM) from endothelial cells (EC) was added to fat derived adipocytes. Additionally, we treated renal interlobar arteries with phenylephrine and dosed cumulative increments of acetylcholine both with and without exposure to CoPP. We did the same vascular reactivity experiments with VECAD-HO-1 lentiviral construct compared to the control. Results: CoPP improved vascular reactivity and decreased adipogenesis compared to the control. MSCs exposed to CM from EC transfected with VECAD-HO-1 showed decreased adipogenesis, smaller lipid droplet size and decreased PPAR-γ, C/EBP and increased Wnt 10b compared to the control. HO-1 upregulation had a direct effect on reducing adipogenesis. This effect was blocked by tin mesoporphrin (SnMP). EC treated with VECAD-HO-1 expressed lower levels of ICAM and VCAM compared to the control, suggesting improved EC function. This also improved ACH induced vascular reactivity. These effects were also reversed by SnMP. The effect of viral transfection was much more specific and sustained than the effects of pharmacologic therapy, CoPP. Conclusion: This study demonstrates that a pharmacological inducer of HO-1 such as CoPP improves endothelial cell function while dampening adipogenesis, but long-term HO-1 expression by direct targeting of endothelial cells by gene transfer therapy may offer a more specific and ideal solution. This was evidenced by smaller healthier adipocytes that had improved insulin sensitivity, suggesting increased adiponectin levels. HO-1 upregulation reestablished the “crosstalk” between perivascular adipose tissue and the vascular system that was lost in the chronic inflammatory state of obesity. This study demonstrates that gene targeting of EC may well be the future direction in treating obesity induced EC dysfunction, with the finding that targeting the vasculature had a direct and sustained effect on adipogenesis.

Carbon monoxide releasing molecule 401 (CORM-401) modulates phase I metabolism of xenobiotics

Next to its well-studied toxicity, carbon monoxide (CO) is recognized as a signalling molecule in various cellular processes. Thus, CO-releasing molecules (CORMs) are of considerable interest for basic research and drug development. Aim of the present study was to investigate if CO, released from CORMs, inhibits cytochrome P450-dependent monooxygenase (CYP) activity and modulates xenobiotic metabolism. CORM-401 was used as a model CO delivering compound; inactive CORM-401 (iCORM-401), unable to release CO, served as control compound. CO release from CORM-401, but not from iCORM-401, was validated using the cell free myoglobin assay. CO-dependent inhibition of CYP activity was shown by 7-ethoxyresorufin-O-deethylation (EROD) with recombinant CYP and HepG2 cells. Upon CORM-401 exposure EROD activity of recombinant CYP decreased concentration dependently, while iCORM-401 had no effect. Treatment with CORM-401 decreased EROD activity in HepG2 cells at concentrations higher than 50 μM CORM-401, while iCORM-401 showed no effect. At the given concentrations cell viability was not affected. Amitriptyline was selected as a model xenobiotic and formation of its metabolite nortriptyline by recombinant CYP was determined by HPLC. CORM-401 treatment inhibited the formation of nortriptyline whereas iCORM-401 treatment did not. Overall, we demonstrate CO-mediated inhibitory effects on CYP activity when applying CORMs. Since CORMs are currently under drug development, the findings emphasize the importance to take into account that this class of compounds may interfere with xenobiotic metabolism.