Carbon Monoxide Metabolism Research Articles

Heme oxygenase, a novel target for the treatment of hypertension and obesity?

Heme oxygenase (HO) is the rate-limiting enzyme in the metabolism of heme-releasing bioactive molecules carbon monoxide (CO), biliverdin, and iron, each with beneficial cardiovascular actions. Biliverdin is rapidly reduced to bilirubin, a potent antioxidant, by the enzyme biliverdin reductase, and iron is rapidly sequestered by ferritin in the cell. Several studies have demonstrated that HO-1 induction can attenuate the development of hypertension as well as lower blood pressure in established hypertension in both genetic and experimental models. HO-1 induction can also reduce target organ injury and can be beneficial in cardiovascular diseases, such as heart attack and stroke. Recent studies have also identified a beneficial role for HO-1 in the regulation of body weight and metabolism in diabetes and obesity. Chronic HO-1 induction lowers body weight and corrects hyperglycemia and hyperinsulinemia. Chronic HO-1 induction also modifies the phenotype of adipocytes in obesity from one of large, cytokine producing to smaller, adiponectin producing. Finally, chronic induction of HO-1 increases oxygen consumption, CO(2), and heat production and activity in obese mice. This review will discuss the current understanding of the actions of the HO system to lower blood pressure and body weight and how HO or its metabolites may be ideal candidates for the development of drugs that can both reduce blood pressure and lower body weight.

Emission of Carbon Monoxide During Composting of Municipal Solid Waste

Elevated concentrations of carbon monoxide (CO) have been observed at the enclosed municipal waste composting facility (ECF) in Edmonton, Canada. Elevated concentrations of CO in an enclosed facility pose a potential health risk to workers. The objectives in this study were to: (1) assess temporal and spatial variability of CO emissions from the composting bays in the ECF using Fourier Transform Infrared (FTIR) spectroscopy; and (2) identify any correlations between the CO emission rate and the physicochemical properties of the compost through bench-scale incubation experiments. Repeated gas measurements were taken above and within the compost bed in the ECF using a probe connected to an FTIR gas analyzer, which continuously collected concentration data. These preliminary field measurements showed maximum CO concentrations of 112 μL−1 within the compost. Autoclaved and non-sterilized compost samples from the ECF were incubated under aerobic and hypoxic conditions, and gas emissions were quantified using gas chromatography (GC). These trials showed a positive correlation between CO emission rate and incubation temperature for all samples, indicating a physico-chemical source of CO generation. Lower concentrations of CO were observed in the non-sterilized compost under both aerobic and anaerobic conditions, presumably due to the microbial metabolism of CO.

Impact of nitric oxide (NO) treatment on the spectroscopic properties and DNA binding activity of the carbon monoxide‐sensing heme transcription factor, CooA

CooA is a carbon monoxide (CO)‐sensing heme transcription factor that regulates CO metabolism in several bacteria including Carboxydothermus hydrogenoformans (Ch). The goal of this research was to investigate the spectroscopic properties and DNA binding activity of Fe(III) Ch CooA that was reacted with NO. Based on electronic absorbance spectra, addition of NO to Fe(III) CooA resulted in the formation of a 6‐coordinate (6‐C) Fe(III)‐NO intermediate species, which slowly converted to a 5‐coordinate (5‐C) Fe(II)‐NO complex. A fluorescence anisotropy assay revealed appreciable DNA binding activity by the 6‐C Fe(III)‐NO form and lesser activity by the 5‐C adduct. DNA binding by 5‐C Fe(II)‐NO CooA was unexpected because this species has a much different coordination structure than the native 6‐C Fe(II)‐CO form or the 6‐C Fe(III)‐NO adduct. Based on these findings, we propose that the most important factor required for activating CooA's DNA binding function is the presence of a gas molecule (CO or NO) that is bound to the correct (i.e. distal) face of the heme. The authors wish to thank the Valparaiso University College of Arts and Sciences for financial support.

Spectroscopic and Functional Characterization of the Nitric Oxide Adducts of the Fe(III) and Fe(II) States of the CO‐Sensing Transcription Factor, CooA, from Carboxydothermus Hydrogenoformans

CooA is a carbon monoxide (CO) sensing transcription factor that is found in several bacteria and regulates CO metabolism. CO binding to CooA's heme groups initiates a conformation change that activates protein DNA binding. This study investigates the reaction of Fe(III) Carboxydothermus hydrogenoformans CooA (Ch CooA) with nitric oxide (NO). Previously, Clark and coworkers reported Fe(II) Ch CooA bound NO to form a 6‐coordinate (6‐C) Fe(II)‐NO adduct that was active for DNA binding in vivo and in vitro. This is in contrast to the best studied CooA homolog from R. rubrum (Rr) that was exquisitely specific for CO and formed an inactive 5‐coordinate (5‐C) Fe(II)‐NO adduct. In the current study, when Fe(III) Ch CooA was incubated with NO, a final 5‐C Fe(II)‐NO species resulted. This species had an electronic absorbance spectrum similar to Rr CooA; however, unlike Rr CooA, the 5‐C Fe(II)‐NO Ch CooA adduct retained some DNA‐binding activity. Results from mutagenesis studies suggest that S‐nitrosylation of a Cys residue located in the heme pocket may account for the unexpected reactivity differences of Fe(III) and Fe(II) Ch CooA with NO. Based on these data, it is proposed the ability of Ch CooA (and failure of Rr CooA) to be activated by NO is due to the binding of NO to the correct (i.e. distal) heme face. The authors wish to thank the Valparaiso University College of Arts and Sciences for financial support.

Carbon Monoxide as an Electron Donor for the Biological Reduction of Sulphate

Several strains of Gram-negative and Gram-positive sulphate-reducing bacteria (SRB) are able to use carbon monoxide (CO) as a carbon source and electron donor for biological sulphate reduction. These strains exhibit variable resistance to CO toxicity. The most resistant SRB can grow and use CO as an electron donor at concentrations up to 100%, whereas others are already severely inhibited at CO concentrations as low as 1-2%. Here, the utilization, inhibition characteristics, and enzymology of CO metabolism as well as the current state of genomics of CO-oxidizing SRB are reviewed. Carboxydotrophic sulphate-reducing bacteria can be applied for biological sulphate reduction with synthesis gas (a mixture of hydrogen and carbon monoxide) as an electron donor.

Ketamine Suppresses LPS-Induced Bile Reflux and Gastric Bleeding in the Rat

Although ketamine has many beneficial effects in a rat model of noninfectious inflammation with lipopolysaccharide (LPS), its effects on gut ileus are unknown. We hypothesized that ketamine would improve LPS-induced ileus and therefore examined its effects on gastric emptying and intestinal transit as well as duodenogastric bile reflux and associated gastric bleeding. Male rats received saline or ketamine (7 mg/kg ip) 1 hour before saline or LPS (20 mg/kg ip) for 5 hours. Thirty minutes before killing, rats received orogastric rhodamine B isothiocyanate-labeled dextran and 5 minutes later fluorescein isothiocyanate-labeled dextran via a duodenal catheter. GI contents were collected for dye, bile acid, and hemoglobin (index of bleeding) determinations. LPS significantly impaired intestinal transit and increased duodenogastric bile reflux and gastric luminal hemoglobin content. Ketamine improved intestinal transit, prevented LPS-induced bile reflux, and diminished gastric bleeding. In mechanistic studies, ketamine also attenuated LPS-induced upregulation of the proinflammatory genes inducible nitric oxide synthase and cyclo-oxygenase-2 in the stomach but preserved expression of the anti-inflammatory gene heme-oxygenase-1 (Western blot). These data suggest that ketamine may prevent LPS-induced gastric bleeding by decreasing bile reflux through improved intestinal transit or by local changes in nitric oxide, prostaglandin, and carbon monoxide metabolism.

Methyl sulfide production by a novel carbon monoxide metabolism in Methanosarcina acetivorans.

We observed dimethyl sulfide and methanthiol production in pure incubations of the methanogen Methanosarcina acetivorans when carbon monoxide (CO) served as the only electron donor. Energy conservation likely uses sodium ion gradients for ATP synthesis. This novel metabolism permits utilization of CO by the methanogen, resulting in quantitative sulfide methylation.

Crystallization and preliminary X-ray analysis of CooA fromCarboxydothermus hydrogenoformans

CooA, a homodimeric haem-containing protein, is responsible for transcriptional regulation in response to carbon monoxide (CO). It has a b-type haem as a CO sensor. Upon binding CO to the haem, CooA binds promoter DNA and activates expression of genes for CO metabolism. CooA from Carboxydothermus hydrogenoformans has been overexpressed in Escherichia coli, purified and crystallized by the vapour-diffusion method. The crystal belongs to space group P2(1), with unit-cell parameters a = 61.8, b = 94.7, c = 92.8 angstroms, beta = 104.8 degrees. The native and anomalous difference Patterson maps indicated that two CooA dimers are contained in the asymmetric unit and are related by a translational symmetry almost parallel to the c axis.

Efeitos ototóxicos da exposição ao monóxido de carbono: uma revisão

Ototoxic effects of carbon monoxide exposure: a review. To analyze the literature on hearing and Carbon Monoxide (CO). To describe the physical properties, the absorption, distribution and metabolism of CO, as well as its origin, production, sources and the international standards for occupational exposure. Several studies about the effects of CO exposure to the auditory system of humans and experimental animals were discussed. The main economic sectors where the combined exposure to noise and CO takes place were identified. A description of the basic CO toxic mechanisms that are able to raise occupational noise-induced hearing loss was given. The review of the literature indicated the following: 1. Examples of CO exposure sources include air pollution, smoking and second-hand smoking, and occupational exposures. 2. CO's main toxic mechanism can lead to hypoxia due to the conversion of oxyhemoglobin to carboxyhemoglobin. 3. Rats have been the most used experimental animals in CO auditory effects studies, this group of studies has demonstrated the combined effects of acute exposure to CO and noise. 4. Studies about the negative effects of CO exposure over the human auditory system were mainly carried out after acute exposures to CO. These studies did not control or report exposure to noise as a contributor to the observed hearing deficits. Currently the available evidence indicates the need for further research on the effects of CO exposure to the auditory system, alone or in combination with noise.

Carbon Monoxide: Endogenous Production, Physiological Functions, and Pharmacological Applications

Over the last decade, studies have unraveled many aspects of endogenous production and physiological functions of carbon monoxide (CO). The majority of endogenous CO is produced in a reaction catalyzed by the enzyme heme oxygenase (HO). Inducible HO (HO-1) and constitutive HO (HO-2) are mostly recognized for their roles in the oxidation of heme and production of CO and biliverdin, whereas the biological function of the third HO isoform, HO-3, is still unclear. The tissue type-specific distribution of these HO isoforms is largely linked to the specific biological actions of CO on different systems. CO functions as a signaling molecule in the neuronal system, involving the regulation of neurotransmitters and neuropeptide release, learning and memory, and odor response adaptation and many other neuronal activities. The vasorelaxant property and cardiac protection effect of CO have been documented. A plethora of studies have also shown the importance of the roles of CO in the immune, respiratory, reproductive, gastrointestinal, kidney, and liver systems. Our understanding of the cellular and molecular mechanisms that regulate the production and mediate the physiological actions of CO has greatly advanced. Many diseases, including neurodegenerations, hypertension, heart failure, and inflammation, have been linked to the abnormality in CO metabolism and function. Enhancement of endogenous CO production and direct delivery of exogenous CO have found their applications in many health research fields and clinical settings. Future studies will further clarify the gasotransmitter role of CO, provide insight into the pathogenic mechanisms of many CO abnormality-related diseases, and pave the way for innovative preventive and therapeutic strategies based on the physiologic effects of CO.

Carbon monoxide and hypertension.

The enzymatic action of heme oxygenase yields carbon monoxide, biliverdin and iron. Carbon monoxide is implicated in many physiological processes, including the regulation of vascular tissue contractility and apoptosis. By stimulating the soluble guanylyl cyclase (sGC)/cGMP pathway and activating K channels in vascular smooth muscle cells (SMCs), carbon monoxide relaxes vascular tissues under physiological conditions. Altered metabolism and functions of carbon monoxide have been linked to the pathogenesis and maintenance of hypertension. The expression and activity of heme oxygenase-1, sGC and cGMP in vascular SMCs are associated with different stages of development of hypertension in spontaneously hypertensive rats (SHRs). The importance of altered heme oxygenase-2 expression in vascular tissues in hypertension remains unclear. Increased vascular contractility, unbalanced cellular apoptosis and proliferation in the vascular wall, increased oxidative stress, and the altered interaction of carbon monoxide and nitric oxide are among the consequences of heme oxygenase/carbon monoxide system dysfunction in hypertension. Acute application of pharmacological inducers to upregulate the expression of heme oxygenase-1 or the use of gene delivery method to overexpress heme oxygenase-1 decreases blood pressure in young SHRs and other animal models of hypertension. These blood pressure-decreasing effects are annulled by metalloporphyrins. In adult SHRs, the heme oxygenase/carbon monoxide system appears to be normalized as a compensatory reaction. To date, acute manipulation of the expression of heme oxygenase-1 has not been successful in decreasing blood pressure in adult SHRs. In conclusion, abnormality of the heme oxygenase/carbon monoxide system has a critical role in the pathogenesis of hypertension, and novel therapeutic approaches should be pursued to achieve selective improvement in the function of this system in hypertension.

Genetic analysis of Carboxydothermus hydrogenoformans carbon monoxide dehydrogenase genes cooF and cooS

Carboxydothermus hydrogenoformans is an extremely thermophilic, Gram-positive bacterium growing on carbon monoxide (CO) as single carbon and energy source and producing only H 2 and CO 2. Carbon monoxide dehydrogenase is a key enzyme for CO metabolism. The carbon monoxide dehydrogenase genes cooF and cooS from C. hydrogenoformans were cloned and sequenced. These genes showed the highest similarity to the cooF genes from the archaeon Archaeoglobus fulgidus and the cooS gene from the bacterium Rhodospirillum rubrum, respectively. The cooS gene was identified immediately downstream of cooF, however, the cooF and cooS genes from C. hydrogenoformans have substantially different codon usage, and the cooF gene Arg codon usage pattern, dominated by AGA and AGG, resembles the archaeal pattern. The data therefore suggest lateral transfer of these genes, possibly from different donor species.

Genetic analysis of Carboxydothermus hydrogenoformans carbon monoxide dehydrogenase genes cooF and cooS.

Carboxydothermus hydrogenoformans is an extremely thermophilic, Gram-positive bacterium growing on carbon monoxide (CO) as single carbon and energy source and producing only H(2) and CO(2). Carbon monoxide dehydrogenase is a key enzyme for CO metabolism. The carbon monoxide dehydrogenase genes cooF and cooS from C. hydrogenoformans were cloned and sequenced. These genes showed the highest similarity to the cooF genes from the archaeon Archaeoglobus fulgidus and the cooS gene from the bacterium Rhodospirillum rubrum, respectively. The cooS gene was identified immediately downstream of cooF, however, the cooF and cooS genes from C. hydrogenoformans have substantially different codon usage, and the cooF gene Arg codon usage pattern, dominated by AGA and AGG, resembles the archaeal pattern. The data therefore suggest lateral transfer of these genes, possibly from different donor species.

Continuous production of mixed alcohols and acids from carbon monoxide

Continuous, steady-state fermentations using carbon monoxide gas as the sole carbon and energy source have been achieved with the CO strain ofButyribacterium methylotrophicum. Fermentation pH was found to regulate carbon monoxide metabolism over the pH range of 6.8 to 5.0. Cell growth diminished at low pH, with washout occurring at pH 5.0. As observed previously in batch culture, lower pH values favored production of butyrate over acetate. The mechanism responsible for this trend is currently being investigated by quantification of key intracellular enzyme activities.

Influence of cyclic AMP on the growth response and anaerobic metabolism of carbon monoxide in Rhodocyclus gelatinosus

Rhodocyclus gelatinosus strain 1 (str. 1), a photoheterotrophic bacterium, used CO as an energy substrate under anaerobic CO/light conditions, and exhibited a diauxic growth response when CO was removed from the culture. Changes in the level of cyclic AMP which occurred in cells during diauxie suggested that the cyclic nucleotide operated as an intracellular control molecule. During CO/light-phase growth, intracellular cyclic AMP was 30 pmol/mg protein, and, as str. 1 adapted for photosynthetic growth after removal of CO, intracellular cyclic AMP levels decreased to 9 pmol/mg protein. Reexposure of a light culture to CO induced synthesis of CO oxidation activity (measured as CO:MV oxidoreductase). If 10 mM cyclic AMP was added with CO, the rate of synthesis of CO:MV oxidoreductase activity increased 25-fold, and str. 1 produced 1,230 units of activity (nmol CO oxidized min-1 mg-1 protein) after only 1 h. With cyclic AMP and no CO, no incerease in CO oxidation activity was seen. Appearance of CO oxidation activity in str. 1 represented de novo protein synthesis and was blocked with chloramphenicol. In addition to stimulating formation of CO oxidative activity, a high level of cyclic AMP in str. 1 during growth with CO appeared to influence photometabolism negatively by repressing bacteriochlorophyll formation.

Metabolism of carbon monoxide by Rhodopseudomonas gelatinosa: cell growth and properties of the oxidation system.

Rhodopseudomonas gelatinosa 1 grew as an anaerobic facultative methylotroph with carbon monoxide as the sole carbon and energy source. Carbon from CO was assimilated into cell material via the ribulose 1,5-bisphosphate carboxylase cycle. The CO oxidation system in R. gelatinosa was induced during growth with the gas substrate. Light-grown cells did not oxidize CO. Surprisingly, when strain 1 cells grown in the dark with CO were transferred to growth with both CO and light, they continued to use CO and then photometabolized after the CO gas flow was stopped. This change in the energy-yielding substrate resulted in a diauxic growth response. The use of CO in preference to light energy forms the basis of a system in the cells that controls photosynthetic differentiation. CO oxidation was assayed as CO-methyl viologen oxidoreductase. Methyl viologen reduction only occurred with CO; the dye was not reduced with other C1 compounds. In vitro methyl viologen was reduced best at 24 degrees C and at pH values above 8.5. Whole cells exhibited a Km of 12.5 microM for CO and a Vmax of 3,800 nmol of CO oxidized per mg of protein per min. This was a low-potential oxidation reaction that readily reduced the viologen dye triquat (1,1'-trimethylene-2,2'-dipyridilium dibromide) (E degrees' = -548 mV).

Metabolism of Carbon Monoxide by the Colonic Flora of Humans

The metabolism of carbon monoxide by the colonic flora was investigated using human fecal homogenates. During anaerobic incubation, these homogenates rapidly consumed added carbon monoxide reducing the PCO level to a minimum of about 0.2 ppm. In the presence of glucose, carbon monoxide consumption averaged about 0.7 ml/h . g feces and without glucose about 0.2 ml/h . g feces. This consumption was not observed if the homogenates were autoclaved, passed through a bacterial filter, or cultured aerobically, indicating that the carbon monoxide was removed by the metabolism of fecal anaerobes. Aerobic incubation of fecal homogenates resulted in slow but definite release of carbon monoxide. While bacterial carbon monoxide consumption probably does not play an appreciable role in the turnover of carbon monoxide that is inhaled or exogenously produced, it is possible that carbon monoxide uptake by colonic flora protects other fecal organisms and possibly the host from carbon monoxide liberated in the gut.

Fetal Smoking

In their fine article concerning the perinatal metabolism of carbon monoxide derived from cigarette smoke, Bureau et al1 speculate that fetal adaptations to cigarette-induced hypoxia may be demonstrable. In fact, Garn et al2,3 have already described such an adaptation: elevated neonatal hemoglobin levels related in a dose-related fashion to maternal cigarette use. The fetus does apparently need to compensate for chronic hypoxia induced by maternal smoking.

Carbon Monoxide Metabolism in Roadside Soils

Air-dried soils which were equilibrated under relative humidities greater than 93% or moistened with liquid water showed marked increases in their capacities to oxidize CO to CO(2). Liquid water addition in excess of saturation resulted in lower CO oxidation rates, reflecting the limited diffusion of CO through the aqueous phase. After 35 days' storage under 100% relative humidity, the capacity for CO oxidation decreased to 21% of the value observed with a freshly collected sample. Incubation of this stored soil under an atmosphere containing 200 ppm of CO (250 mg/m) for 21 days resulted in a sevenfold increase in CO oxidation. A correlation was noted between the CO oxidative activity and the history of previous exposure of soils to high ambient levels of CO. The organisms responsible for CO oxidation apparently comprise a small fraction of the microbial population in the soils. With a roadside soil the oxidation of CO provided the driving force for the assimilation of CO(2). The stoichiometry of the oxidative and assimilatory reactions in soil was in the range of values reported from laboratory studies with CO chemoautotrophs (carboxydobacteria). It is proposed that the population and activity of CO-oxidizing microorganisms increase in response to increasing levels of CO in the environment.

Microbial metabolism of carbon monoxide in culture and in soil.

Nocardia salmonicolor readily oxidized CO to CO2. Slight activity was found among species of Actinoplanes, Agromyces, Microbispora, Mycobacterium, and other nocardias, and no oxidation was detected in the algae, fungi, and other bacteria tested. Carbon monoxide was oxidized rapidly to CO2 in the dark in two soils incubated in air or under flooded conditions, but little of the 14C from 14CO was incorporated into the organic fraction of these soils. The reaction was microbial because appreciable CO was not converted to CO2 in autoclaved or gamma-irradiated soil. Heating the soil for 25 min at 70 degrees C destroyed its CO-oxidizing activity. The incorporation of 14CO2 into the cells of microorganisms in soil and soil suspension was not enhanced by incubating the samples in the presence of CO, suggesting that CO oxidation was not the result of autotrophic metabolism. The oxidation of 17 mu 1 of CO per liter in the head space was nearly complete in 6 h in soil incubated in air or anaerobically.