Endogenous Carbon Monoxide Production Research Articles

Carboxyhemoglobin Elevation Due to Hemolytic Anemia

A critically ill man with drug-induced hemolytic anemia and hepatic failure was hospitalized at a private academic medical center in Seattle, Washington. Intravascular hemolysis with associated endogenous carbon monoxide (CO) production resulted in elevation of the patient’s carboxyhemoglobin (COHb) level to as high as 9.7%. Serial measurements of the patient’s COHb level were obtained and compared with other conventional measures of hemolytic activity. With the availability of new non-invasive measurement technology to detect COHb elevations, emergency clinicians are likely to see COHb elevation as a manifestation of hemolytic anemia.

Membrane potential gradient is carbon monoxide-dependent in mouse and human small intestine

The aims of this study were to quantify the change in resting membrane potential (RMP) across the thickness of the circular muscle layer in the mouse and human small intestine and to determine whether the gradient in RMP is dependent on the endogenous production of carbon monoxide (CO). Conventional sharp glass microelectrodes were used to record the RMPs of circular smooth muscle cells at different depths in the human small intestine and in wild-type, HO2-KO, and W/W(V) mutant mouse small intestine. In the wild-type mouse and human intestine, the RMP of circular smooth muscle cells near the myenteric plexus was -65.3 +/- 2 mV and -58.4 +/- 2 mV, respectively, and -60.1 +/- 2 mV and -49.1 +/- 1 mV, respectively, in circular smooth muscle cells at the submucosal border. Oxyhemoglobin (20 microM), a trapping agent for CO, and chromium mesoporphyrin IX, an inhibitor of heme oxygenase, abolished the transwall gradient. The RMP gradients in mouse and human small intestine were not altered by N(G)-nitro-l-arginine (200 microM). No transwall RMP gradient was found in HO2-KO mice and W/W(V) mutant mice. TTX (1 microM) and 1H-[1,2,4-]oxadiazolo[4,3-a]quinoxalin-1-one (10 microM) had no effect on the RMP gradient. These data suggest that the gradient in RMP across the thickness of the circular muscle layer of mouse and human small intestine is CO dependent.

Autonomic Cardiovascular Responses to Heme Oxygenase Inhibition in Conscious Rats

Carbon monoxide (CO) is produced in the course of heme degradation from biliverdin by heme oxygenase (HO) in various tissues, including the central nervous system. Recent studies suggest the inhibition of HO activity increases arterial pressure mediated by the autonomic nervous system. The present study was designed to investigate the autonomic regulation of cardiovascular responses to inhibition of endogenous CO production by the HO inhibitor Zinc deuteroporphyrin 2, 4-bis glycol (ZnDPBG) by using direct sympathetic nerve recordings in conscious, chronically instrumented rats. ZnDPBG induced increases in mean arterial pressure (MAP) (P<0.05) and renal sympathetic nerve activity (RSNA) (P<0.05) but no significant change in heart rate (P>0.05) in intact rats. In atropine-treated rats, ZnDPBG also induced increases in MAP (P<0.05) and RSNA (P<0.05) but no change in heart rate (P>0.05). In sinoaortic denervated rats, ZnDPBG induced increases in MAP (P<0.05), heart rate (P<0.05), and RSNA (P<0.05). ZnDPBG shifted the baroreflex curve for RSNA upward and to the right, which was characterized by increases in the maximum and minimum response and midpoint pressure without altering the maximum gain. These results indicate that inhibition of HO activity within the central nervous system causes sympathoexcitation, resulting in an increase in arterial pressure. We conclude that the CO/HO system plays an important role in cardiovascular regulation by modulating sympathetic tone.

PPARα agonist protects against salt‐mediated increases in endogenous carbon monoxide production and blood pressure in Dahl salt‐sensitive rats

Heme oxygenase (HO) metabolizes heme to form carbon monoxide (CO). Increased heme-derived CO inhibits nitric oxide synthase and promotes hypertension in Dahl salt-sensitive rats (DS). Peroxisome proliferator-activated receptor α (PPARα) agonists confer cardiovascular protection during hypertension and lower blood pressure in DS. The current study tests the hypothesis that the PPARα agonist fenofibrate prevents the high salt (HS)-diet induced increase in endogenous CO production and blood pressure in DS. Male DS were placed on low (0.3% NaCl, LS) or HS (8% NaCl) diets and some received 90mg/kg/day fenofibrate in the drinking water. Respiratory CO excretion and blood pressure were measured weekly via solid-phase gas chromatography and tail-cuff plethysmography. CO excretion (HS: Δ +0.57±0.07 μmol/hr per kg) and systolic blood pressure (HS: 132±4 to 251±5 mmHg) increased markedly in HS rats. Fenofibrate treatment attenuated the HS diet induced increase in CO excretion (Δ+0.07±0.01 μmol/hr per kg) and blood pressure (145±4 to 172±8 mmHg). These data show that a PPARα agonist protects from HS diet-induced increases in CO production and blood pressure in DS. These results suggest that PPARα agonists might exert their blood pressure lowering effect by “normalizing” endogenous CO production in DS. Supported by NIH/NCRR grant P20 RR017659 (FKJ), NIH/NHLBI RO1 grants HL76187 (RAJ), HL59976 (WD) and HL74966 (WD).

Mouse cerebral arteries dilate to carbon monoxide

Carbon monoxide (CO) is produced endogenously by heme oxygenase (HO) and CO is a vasodilator in some vessel beds. The constitutive isoform of HO, HO-2, is normally present in the vasculature, including cerebral vessels. In the cerebral vasculature CO dilates in some species (i.e. piglet) but not in others (i.e. rat). We investigated cerebrovascular function, including responses to CO and to inhibition of HO, in the middle cerebral artery (MCA) of both wild-type (w.t.) and HO-2 deficient (KO) mice. Dilation to UTP (10−4 M) in isolated, pressurized, and perfused MCAs preconstricted with phenlyephrine (PE) was similar in w.t. and KO mice (96±4% vs 96±5% respectively). Interestingly, inhibition of nitric oxide (NO) synthase and cyclooxygenase did not alter dilation to UTP in either genotype. Constriction to PE (10−6 M to 10−4 M) was also virtually identical in both genotypes reaching a maximum of 36±2% in w.t. and 33±3% in KO mice. Dilation to authentic NO (10−10 M to 10−7 M) reached a maximum of 59±9% in w.t. mice at 10−7 M, and was a similar 62±4% in KO mice. CO (10−7 M to 10−4 M) dose-dependently dilated the MCA of both w.t. and KO mice reaching 71±10% and 54±9% respectively. The HO inhibitor, Cr(III) mesoporphyrin IX (10−5 M), did not alter vascular diameter in either genotype. The heme precursor, δ-aminolevulinic (δ-ALA), acid caused dilation of some, but not all w.t. MCAs, whereas no MCA from KO mice dilated to δ-ALA. Thus, exogenous CO is capable of dilating the mouse MCA, however, the endogenous production of CO does not appear to be an important mediator of vascular function in the mouse MCA. This work was supported by F32 HL080916-01 and T32 HL072754.

High‐salt diet increases endogenous carbon monoxide production to promote hypertension in Dahl salt‐sensitive rats

High‐salt diet increases endogenous carbon monoxide production to promote hypertension in Dahl salt‐sensitive rats

Carbon monoxide protects PC12 cells from peroxynitrite-induced apoptotic death by preventing the depolarization of mitochondrial transmembrane potential

Heme oxygenase-1 (HO-1), the rate-limiting enzyme in catalyzing heme degradation into biliverdin, free iron, and carbon monoxide (CO), serves as a protective enzyme against oxidative and nitrosative stresses. In the present study, we investigated the cytoprotective effects of HO-1 upregulation and its product CO against the peroxynitrite-induced PC12 cell death. PC12 cells treated with 3-morphoinosydonimine (SIN-1), a generator of peroxynitrite (ONOO −), underwent apoptotic cell death as evidenced by dissipation of mitochondrial transmembrane potential (ΔΨm), release of mitochondrial cytochrome c into cytoplasm, cleavage of poly(ADP-ribose)polymerase and fragmentation of internucleosomal DNA. Pretreatment of PC12 cells with a low non-toxic concentration of SIN-1 (0.5 mM) induced HO-1 expression and abrogated the cell death caused by subsequent challenge with high dose SIN-1 (2.5 mM). Furthermore, pretreatment of PC12 cells with SnCl 2, a potent inducer of HO-1 expression, increased endogenous production of CO (HO activity) and rescued the PC12 cells from peroxynitrite-induced apoptosis. The cytoprotective effect of SnCl 2 was abolished when the HO activity was inhibited by zinc protoporphyrin IX (ZnPP IX). PC12 cells treated directly with the CO-releasing molecule, tricarbonyldichlororuthenium (II) dimer ([Ru(CO) 3Cl 2] 2) became tolerant to the depolarization of ΔΨm and apoptosis induced by high dose peroxynitrite. Taken together, these data demonstrate that the adaptive protection against peroxynitrite-induced apoptotic death in PC12 cells is mediated by CO formed as a consequence of HO-1 induction.

Effects of carbon monoxide and heme oxygenase inhibitors in cerebral vessels of rats and mice

Carbon monoxide (CO) has been postulated to be a signaling molecule in many tissues, including the vasculature. We examined vasomotor responses of adult rat and mouse cerebral arteries to both exogenously applied and endogenously produced CO. The diameter of isolated, pressurized, and perfused rat middle cerebral arteries (MCAs) was not altered by authentic CO (10(-6) to 10(-4) M). Mouse MCAs, however, dilated by 21 +/- 10% at 10(-4) M CO. Authentic nitric oxide (NO., 10(-10) to 10(-7) M) dilated both rat and mouse MCAs. At 10(-8) M NO., rat vessels dilated by 84 +/- 4%, and at 10(-7) M NO., mouse vessels dilated by 59 +/- 9%. Stimulation of endogenous CO production through heme oxygenase (HO) with the heme precursor delta-aminolevulinic acid (10(-10) to 10(-4) M) did not dilate the MCAs of either species. The metalloporphyrin HO inhibitor chromium mesoporphyrin IX (CrMP) caused profound constriction of the rat MCA (44 +/- 2% at 3 x 10(-5) M). Importantly, this constriction was unaltered by exogenous CO (10(-4) M) or CO plus 10(-5) M biliverdine (both HO products). In contrast, exogenous CO (10(-4) M) reversed CrMP-induced constriction in rat gracilis arterioles. Control mouse MCAs constricted by only 3 +/- 1% in response to 10(-5) M CrMP. Magnesium protoporphyrin IX (10(-5) M), a weak HO inhibitor used to control for nonspecific effects of metalloporphyrins, also constricted the rat MCA to a similar extent as CrMP. We conclude that, at physiological concentrations, CO is not a dilator of adult rodent cerebral arteries and that metalloporphyrin HO inhibitors have nonspecific constrictor effects in rat cerebral arteries.

Endogenous carbon monoxide production correlates weakly with severity of acute illness

The enzyme haeme oxygenase-1 is highly inducible by oxidative agents. Its product carbon monoxide is thought to exert anti-inflammatory properties. We recently showed, that critically ill patients produce higher amounts of carbon monoxide compared to healthy controls. In the present study we compare endogenous carbon monoxide production with the severity of illness of intensive care unit patients. Exhaled carbon monoxide concentration was measured in 95 mechanically ventilated, critically ill patients (mean age +/- SD, 59.5 +/- 15.7) on a carbon monoxide monitor. Measurements were taken every hour for 24 h in each patient. Data were analysed using Mann-Whitney rank sum test. Correlation analysis was performed with the Spearman's rank order correlation. Carbon monoxide production correlated weakly with the multiple organ dysfunction score (R = 0.27; P = 0.009). Patients suffering from cardiac disease (median 22.5, interquartile range 16.2-27.4 microL kg(-1) h(-1) vs. median 18.2, interquartile range 14.2-21.8 microL kg(-1) h(-1), P = 0.008) and critically ill patients undergoing dialysis (median 25.0, interquartile range 21.4-30.2 microL kg(-1) h(-1), vs. median 19.4, interquartile range 14.7-23.3 microL kg(-1) h(-1), P = 0.004) produced significantly higher amounts of carbon monoxide compared to critically ill controls. The findings suggest that endogenous carbon monoxide production might reflect the severity of acute organ dysfunction.

CO from enhanced HO activity or from CORM-2 inhibits both O 2− and NO production and downregulates HO-1 expression in LPS-stimulated macrophages

Carbon monoxide (CO) arising from heme degradation, catalyzed particularly by the stress-inducible heme oxygenase-1 (HO-1), has recently been demonstrated to provide cytoprotection against cell death in macrophages stimulated with bacterial lipopolysaccharide (LPS). In the present study, we determined the effects of CO on the production of reactive oxygen species (ROS) and nitric oxide (NO) by the LPS-stimulated RAW 264.7 macrophages. In addition, effect of CO-exposure on the production of superoxide (O 2 −) in the phorbol myristate acetate (PMA)-stimulated PLB-985 neutrophils was determined. Production of ROS by the LPS-stimulated macrophages pretreated with 50 μM [Ru(CO) 3Cl 2] 2, a CO-releasing molecule (CORM-2), was abolished and the production of O 2 − by the PMA-stimulated neutrophils pretreated with the CORM-2 was decreased markedly. The CORM-2 (50 μM) was not cytotoxic to both the unstimulated and LPS-stimulated macrophages when determined by employing mitochondrial reductase function test (MTT assay). In macrophages pretreated with increasing doses of CORM-2, both the LPS-derived upregulations of iNOS (NO production) and HO-1 expression (CO production) were suppressed in a dose-dependent manner. Alternatively, when the macrophages were treated with LPS and CO-donor together, the LPS-derived increase in NO production was decreased. Conversely, when the control and LPS-stimulated macrophages were treated with zinc protoporphyrin IX (ZnPP) to inhibit the HO activity blocking endogenous production of CO (basal and enhanced), macrophages died extensively. Interestingly, production of NO in the LPS-stimulated macrophages increased significantly following the ZnPP treatment. Addition of CORM-2 to the LPS-treated cells that were being treated additionally with ZnPP did not prevent the cell death. However, endogenous overproduction of CO by super-induction of HO-1 (obtained by pretreatment of macrophages with either buthionine sulfoximine or hemin) decreased the LPS-derived iNOS expression without affecting cell survival. Combined, these results indicated that enhanced HO activity is essential for the survival of LPS-stimulated macrophages. Thus, upregulation of HO-1 and overproduction of CO may allow the survival of LPS-stimulated macrophages; first, by eliminating the free heme to prevent Fenton reaction, second, by limiting the availability of free heme required for induction of NO-producing heme enzyme (i.e., iNOS), third, by limiting additional production of O 2 − and NO via CO-derived inhibition on the activities of heme enzymes like NADPH oxidase and iNOS, respectively. CO may allow the LPS-activated macrophages to return back to the normal quiet state insensitive to additional stimuli causing oxidative stress.

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.

Metabolic syndrome increases endogenous carbon monoxide production to promote hypertension and endothelial dysfunction in obese Zucker rats

Vascular heme oxygenase (HO) metabolizes heme to form carbon monoxide (CO). Increased heme-derived CO inhibits nitric oxide synthase and can contribute to hypertension via endothelial dysfunction in Dahl salt-sensitive rats. Obese Zucker rats (ZR) are models of metabolic syndrome. This study tests the hypothesis that endogenous CO formation is increased and contributes to hypertension and endothelial dysfunction in obese ZR. Awake obese ZR showed increased respiratory CO excretion, which was lowered by HO inhibitor administration [zinc deuteroporphyrin 2,4-bis glycol (ZnDPBG) 25 micromol.kg(-1).24 h(-1) ip]. In awake obese ZR, chronically instrumented with femoral arterial catheters, blood pressure was elevated but was decreased by the HO inhibitor ZnDPBG. Body weight, blood glucose, glycated hemoglobin, plasma insulin, total and LDL cholesterol, oxidized LDL, and triglyceride levels were elevated in obese ZR, and, except for LDL cholesterol, were unchanged by HO inhibition. Total HO-1 protein levels were not different between lean and obese ZR aortas. In vitro experiments used isolated skeletal muscle arterioles with constant pressure and no flow, or constant midpoint, but altered endpoint pressures to establish graded levels of luminal flow. In obese ZR arterioles, responses to ACh and flow were attenuated. Acute in vitro pretreatment with an HO inhibitor, chromium mesoporphyrin, enhanced ACh and flow-induced dilation and abolished the differences between groups. Furthermore, exogenous CO prevented the restoration of flow-induced dilation by the HO inhibitor in obese ZR arterioles. These results suggest that HO-derived CO production is increased and promotes hypertension and arteriolar endothelial dysfunction in obese ZR with metabolic syndrome independent of affecting metabolic parameters.

Interactions between the heme oxygenase, cyclooxygenase and nitric oxide synthase pathways in the regulation of the resting hypothalamic blood flow

The heme-oxgenase (HO) – carbon monoxide (CO) pathway has been reported to evoke direct vascular effects and to influence other vasoregulatory mechanisms like the cyclooxygenase (COX) and nitric oxide synthase (NOS) systems. Since the hypothalamus expresses relatively high HO, COX and NOS levels compared to other brain regions, we have hypothesized interactions among these pathways in the regulation of the resting local hypothalamic tissue blood flow (HBF). Therefore, we have investigated whether inhibition of the COX and NOS pathways influences the alterations of the HBF that develop after HO blockade. Adult male Wistar rats were anaesthetized with 1.3 g/kg urethane. The femoral arteries were cannulated for measurement of the mean arterial pressure (MAP) and for blood sampling. HBF was measured by use of the hydrogen gas-clearance method. HO-blockade was induced by ip. injection of 45 imol/kg zinc deuteroporphyrin 2,4-bis glycol (ZnDPBG). In the first group of the animals HBF, MAP and blood gas measurements were performed under physiological conditions. In the second and third experimental groups the animals received diclofenac (10 mg/kg iv.) or NG-nitro-L-arginine methyl ester (L-NAME, 50 mg/kg iv.) pretreatment in order to inhibit prostanoid- or NO-synthesis, respectively. In the fourth group the animals received combined diclofenac and L-NAME pretreatment. In all groups HBF values were determined before and after the pretreatment as well as after the induction of HO-blockade. Baseline arterial pO2, pCO2 and pH values were within the physiological range and did not change throughout the experiments. In animals pretreated with L-NAME or with diclofenac+L-NAME the MAP was significantly higher (1435 mmHg and 1386 mmHg, respectively) than in controls (995 mmHg) or after diclofenac pretreatment alone (957 mmHg). ZnDPBG administration, however, did not influence the MAP in any of the experimental groups. L-NAME and diclofenac+L-NAME pretreatments markedly reduced the HBF (from 0.900.10 to 0.550.09 ml/g/min and from 0.790.11 to 0.440.11 ml/g/min, respectively) while diclofenac alone had no significant effect (0.840.09 vs. 0.880.10 ml/g/min). ZnDPBG administration in control animals did not influence the HBF (-0.34.1 %), but significantly increased it by 15.52.9 % after diclofenac pretreatment. In contrast, ZnDPBG induced a marked reduction (-20.65.6 %) of the HBF in animals pretreated with L-NAME. In animals receiving both diclofenac and L-NAME pretreatment the HBF remained unchanged after ZnDPBG administration (+5.95.4 %). Our observations indicate that the HO pathway interacts with both the COX and the NOS systems in the regulation of the hypothalamic circulation. Endogenous CO production appears to increases the HBF via a COX-dependent mechanism, but at the same time suppresses NOS activity which leads to the reduction of HBF. These effects of CO may neutralize each other under physiological conditions. In pathophysiological states, however, which are associated with altered COX or NOS activity, the HO pathway may significantly influence the resting CBF.

Inhibition of endogenous carbon monoxide production induces transient retention losses in the day-old chick when trained using a single trial passive avoidance learning task

Carbon monoxide (CO) is most often thought of as an exogenous toxin rather than as a possible endogenous nootrope. However, a limited number of studies have suggested that CO is necessary in memory processing for at least some tasks. While nitric oxide (NO) and CO are known activators of guanylyl cyclase (GC), only the effect of NO on GC has been extensively investigated as a mechanism underlying memory processing. The aim of the present study was to determine if inhibition of CO production would have an effect on memory processing. Using chicks trained on a single trial passive avoidance task, inhibition of CO production using zinc (II) deuteroporphyrin IX 2,4-bis ethylene glycol (ZnBG; 5 μM) resulted in two transient retention losses occurring at around 40 and 130 min post-training. The timing of these transient retention losses was similar to those observed following inhibition of GC, using the same species and task in a previous study. This supports the notion that CO is necessary in memory processing for this task and may act through a GC-dependent mechanism. As ZnBG also directly inhibits GC or nitric oxide synthase (NOS) at high concentrations, a second experiment was carried-out to confirm the specificity of ZnBG for heme oxygenase (HO) at the concentration used. The action of ZnBG was challenged with the HO agonist hemin (100 μM) and the transient deficits were abolished. This confirmed that the action of ZnBG on memory was through a CO-related mechanism rather than directly on GC or NOS. In this way the specificity of ZnBG (5 μM) for HO could be confirmed. The results support a role for endogenous CO in memory processing, possibly through activation of GC. In addition, the transient retention losses observed following administration of ZnBG suggest that CO may be necessary for memory retrieval and not formation as previously thought.

Exhaled CO After Surgery: A Consequence of Postoperative Narcotics?

To the Editor: Hayashi et al. (1) attribute increased exhaled carbon monoxide (CO) or carboxyhemoglobin (COHb) concentrations after surgery and anesthesia to increased production from stress-induced activation of heme oxidase. Many factors may confound this relationship. Oxygen at 4.0 L/min was administered postoperatively, but the resulting inspired oxygen concentrations (Fio2) during gas sampling were not reported. Because exhaled CO concentrations vary with Fio2 at the same COHb (2–4), errors of attribution may result. Intraoperatively, increased Fio2 may speed CO elimination and reduce COHb, introducing additional errors of attribution. Second, at the same endogenous production rate and Fio2, alveolar ventilation is inversely related to COHb once a new steady state is achieved. The half-life of CO averages 4 h, but ranges from 23 min to 11 h with extremes of ventilatory parameters (2). If mechanical ventilation increased alveolar ventilation, CO and COHb may decrease from increased elimination. If narcotics depressed spontaneous ventilation intraoperatively or postoperatively, CO and COHb may increase, rendering them poor markers of endogenous CO production. Third, regardless of minute ventilation, rebreathing during low flow anesthesia may increase CO and COHb via impaired elimination (3–5). The authors do not provide necessary data to calculate rebreathing, nor was rebreathing controlled during the study. Fourth, there was no control group. The observed changes may result from systematic pharmacokinetic alterations, requiring a nonoperative control group. Alternatively, since the CO production rate = elimination rate + accumulation, the production rate can be calculated from timed expiratory gas collections and COHb measurements. The authors must demonstrate that their results transcend mere pharmacokinetic effects of Fio2, rebreathing, and alveolar ventilation. Finally, one should determine whether metabolism of extravasated blood or transfused, senescent red cells could account for any actual increased CO production. Marshall B. Dunning III, PhD, MS Division of Pulmonary/Critical Care Medicine Medical College of Wisconsin [email protected] Harvey J. Woehlck, MD Department of Anesthesiology Medical College of Wisconsin Milwaukee, WI

Does Carboxy-hemoglobin Serve as a Stress-induced Inflammatory Marker Reflecting Surgical Insults?

Endogenous carbon monoxide (CO) production has been recently observed to be an index of the inflammatory response, reflecting various insults in critically ill patients. Major surgery is supposed to modulate the production of CO by transcriptional regulation of heme oxygenase (HO). CO is easy to measure as carboxyhemoglobin (CO-Hb) by spectrophotometry; however, whether CO-Hb can be used as an index reflecting surgical insults is unknown. We investigated changes in CO generation during coronary artery bypass graft by measuring CO-Hb concentrations and the expression of HO in circulating blood as well as the expressions of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta). The expression ratios of heme oxygenase-1 (HO-1), TNF-alpha, and IL-1 beta significantly increased after surgery, and these values correlated significantly with one another. CO-Hb concentrations significantly increased after surgery; however, many of those values during artificial ventilation with high inspired oxygen fraction were within normal limits. Furthermore, changes in CO-Hb concentrations were small when preoperative values were high. On the whole, CO-Hb concentrations significantly but weakly correlated with the expression ratios of the inflammatory mediators. However, they did not correlate in the patients who showed higher preoperative CO-Hb concentrations. These data indicate that CO-Hb concentrations can, in general, reflect the inflammatory response induced by surgical insult; however, CO-Hb measurement may not be a useful form of clinical monitoring because of the limited degree of changes, the variation of baseline values, and the necessity for the management under fixed conditions.

Heme oxygenase-1-related carbon monoxide and flavonoids in ischemic/reperfused rat retina.

There is increasing evidence to show cytoprotective effects of various flavonoid-rich extracts and the tissue-protective capacity of flavonoid-rich extract of sour cherry is due to flavonoid components of seeds. Sour cherry seed flavonoids were evaluated for their contribution to postischemic recovery related to endogenous carbon monoxide (CO) production in rat retinas subjected to ischemia/reperfusion. Rats were orally treated with selected doses of flavonoid-rich extract of sour cherry seeds for 2 weeks. Animals were anesthetized, and a suture was placed behind the globe including the central retinal artery. Next, retinas were subjected to 90 minutes of ischemia followed by 24 hours of reperfusion. After this procedure, heme oxygenase-1 (HO-1)-related protein expression and enzyme activity, HO-1-related endogenous CO production, and ionic imbalance including tissue Na(+), K(+), and Ca(2+) in untreated and treated ischemic/reperfused retinas were measured. Retinal ischemia/reperfusion resulted in a significant reduction (to 10%) in HO-1 protein expression, enzyme activity, and HO-1-related endogenous CO production in the retina. These changes were accompanied by increases in retinal Na(+) and Ca(2+) gains and loss of K(+). In rats treated with 10 and 30 mg/kg of sour cherry flavonoid-rich extract, after 24 hours of reperfusion, tissue Na(+) and Ca(2+) accumulation and K(+) loss were prevented in comparison with the drug-free control. Sour cherry seed flavonoid-rich extract showed a protective effect against reperfusion-induced injury through its ability to reduce the changes in concentrations of retinal ions through HO-1-related endogenous CO production in the ischemic/reperfused retina.

Endogenous carbon monoxide production correlates with severity of acute illness

Department of Anaesthesiology and Intensive Care Medicine, University Hospital Muenster, Muenster, Germany

Carbon monoxide paradoxically protects against hypoxia

Background: Tissue hypoxia is fundamental to the development of cellular injury caused by multiple processes, including hemorrhagic shock. Others and we have previously demonstrated that endogenous production of carbon monoxide (CO) by heme oxygenase or exogenous administration of CO can protect against organ injury induced by hemorrhage. The purpose of these experiments was to test the hypotheses that CO abrogates the development of tissue hypoxia in vivo and diminishes effects of hypoxia in vitro.Methods: Male C57/BL6 mice were hemorrhaged to a mean arterial pressure of 25 mmHg. Control animals underwent the same procedure but were not hemorrhaged (sham). Inhalational CO exposure (250 ppm) was initiated concurrently with hemorrhage Mice were administered EF5 (10 μl/g; ip), which is an agent that irreversibly binds to intracellular proteins under hypoxic conditions and can then be detected by immunohistochemistry. Mice were sacrificed after 75 minutes of shock and livers were harvested. For in vitro experiments, primary mouse hepatocytes were exposed to normoxia (21% O2) or hypoxia 1% O2) with and without CO (250 ppm). Cells were harvested and assayed for viability, ATP content, or VEGF production. Results: Untreated hemorrhaged mice had a 17-fold increase in EF5 staining compared to shams. Hepatic hypoxia was most pronounced around the central veins. CO-treated hemorrhaged mice had a 79±13% reduction in EF5 staining compared to untreated hemorrhaged mice (P < 0.05). Additionally, CO-treated sham mice demonstrated no significant liver hypoxia. In vitro, CO significantly protected against hypoxia-induced cell death (P < 0.05). Hepatocytes exposed to hypoxia demonstrated a 54 ± 4% reduction in intracellular ATP levels after 6 hours, whereas CO treatment of hypoxic cells resulted in only a 9 ± 3% reduction in ATP (P < 0.01). Likewise, CO significantly inhibited VEGF elaboration by hypoxic hepatocytes. Conclusions: Inhaled low dose CO can paradoxically abrogate liver hypoxia during hemorrhage. Additionally, CO diminishes the consequences of hypoxia in vitro. CO may exert these effects by decreasing cellular metabolic activity and oxygen requirements, though further investigation is required. CO may prove to be a useful clinical adjunct in the treatment of hemorrhagic shock.

Dysregulation of endogenous carbon monoxide and nitric oxide production in patients with advanced ischemic or nonischemic cardiomyopathy

Carbon monoxide (CO) and nitric oxide (NO) are endogenous vasoregulatory molecules whose role in heart failure is not fully known. Exhaled CO and NO measurement provide novel noninvasive assessment of their endogenous production. We compared exhaled CO and NO in 24 patients with advanced ischemic and nonischemic cardiomyopathy and in 13 control subjects without known cardiac disease at rest and at 1 and 5 minutes after exercise testing. Exhaled CO was lower in patients with cardiomyopathy at rest (1.66 ± 0.2 vs 1.80 ± 0.5 ppm, p = 0.02) and 1 minute after exercise (1.35 ± 0.2 vs 1.81 ± 0.5 ppm, p = 0.009), with a similar trend at 5 minutes after exercise (1.45 ± 0.3 vs 1.81 ± 0.5 ppm, p = 0.14). Exhaled CO decreased in patients with cardiomyopathy after exercise (p <0.001 and p = 0.02 at rest vs 1 and 5 minutes after exercise, respectively) but was maintained in controls. Exhaled NO did not differ between patients with cardiomyopathy and controls at rest (9.48 ± 1.4 vs 9.68 ± 1.5 ppb, p = NS) and after exercise (1 minute: 10.91 ± 1.8 vs 9.19 ± 1.2 ppb; 5 minutes: 10.52 ± 1.5 vs 8.90 ± 1.2 ppb, p = NS). Exhaled NO increased after exercise in patients with cardiomyopathy (p = 0.01 and p = 0.04 rest vs exercise at 1 and 5 minutes, respectively), but was maintained in controls. Exhaled CO and NO were not correlated with peak oxygen consumption in patients with cardiomyopathy. The differential responses in exhaled CO and NO at rest or with exercise between patients with cardiomyopathy and normal controls may point to dysregulation in endogenous CO and NO production.