Endogenous carbon monoxide production in disease

Forensic utility of carboxyhemoglobin levels in postmortem spleen specimens in South Korea

In order to determine whether CO poisoning was the definitive cause of death, the concentration of carboxyhemoglobin (COHb) in spleen specimens was analyzed using a gas chromatography-thermal conductivity detector. 125 cases of forensic autopsy reports containing COHb analysis requests were analyzed and subdivided into two groups, improbable and highly probable of CO intoxication. In the first group which consists of 100 cases, the results of COHb analysis were negative, and the circumstances of death, as well as the postmortem findings could not validate the exposure to CO. In the second group which consists of 25 cases, the results of COHb were positive, and both postmortem findings and circumstances of death confirmed the exposure to CO. In the cases of indoors and vehicle fires or those including the use of briquettes, COHb levels reached 43.1-97.5 %, whereas in individuals without any feature of CO poisoning had COHb level high as 29.8 %. However, certain cases without any connection to fire nor CO exposure also contained significant amount of CO based on post-mortem analysis. This study focuses on cases without any relationship to fire or CO and proves that COHb levels below 30 % may be considered as a contributing factor to but not exclusively as the cause of death.

Carboxyhemoglobin as Potential Biomarker for Cardiac Surgery Associated Acute Kidney Injury

OBJECTIVES

Carboxyhemoglobin (CO-Hb) is a marker of hemolysis and inflammation, both risk factors for cardiac surgery-associated AKI (CSA-AKI). However, the association between CO-Hb and CSA-AKI remains unknown.

DESIGN

A retrospective cohort study.

SETTING

Tertiary university-affiliated metropolitan hospital: single center.

PARTICIPANTS

Adult on-pump cardiac surgery patients from July 2014 to June 2022 (N = 1,698).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Patients were stratified into quartiles based on CO-Hb levels at intensive care unit (ICU) admission. A progressive increased risk of CSA-AKI was observed with higher CO-Hb levels at ICU admission. On multivariable logistic regression analysis, the highest quartile (CO-Hb ≥ 1.4%) showed an independent association with the occurrence of CSA-AKI (odds ratio 1.45 compared to the lowest quartile [CO-Hb < 1.0%], 95% CI 1.023-2.071; p = 0.038). Compared to patients with CO-Hb <1.4%, patients with CO-Hb ≥ 1.4% at ICU admission had significantly higher postoperative creatinine (135 vs 116 μmol/L, p < 0.001), higher rates of postoperative RRT (6.7% vs 2.3%, p < 0.001) and AKI (p < 0.001) on univariable analysis and shorter time to event for AKI or death (p < 0.001).

CONCLUSIONS

CO-Hb ≥ 1.4% at ICU admission is an independent risk factor for CSA-AKI, which is easily obtainable and available on routine arterial blood gas measurements. Thus, CO-Hb may serve as a practical and biologically logical biomarker for risk stratification and population enrichment in trials of CSA-AKI prevention.

Carbon Monoxide as a Potential Therapeutic Agent: A Molecular Analysis of Its Safety Profiles

Carbon monoxide (CO) is endogenously produced in mammals, with blood concentrations in the high micromolar range in the hemoglobin-bound form. Further, CO has shown therapeutic effects in various animal models. Despite its reputation as a poisonous gas at high concentrations, we show that CO should have a wide enough safety margin for therapeutic applications. The analysis considers a large number of factors including levels of endogenous CO, its safety margin in comparison to commonly encountered biomolecules or drugs, anticipated enhanced safety profiles when delivered via a noninhalation mode, and the large amount of safety data from human clinical trials. It should be emphasized that having a wide enough safety margin for therapeutic use does not mean that it is benign or safe to the general public, even at low doses. We defer the latter to public health experts. Importantly, this Perspective is written for drug discovery professionals and not the general public.

Carboxyhemoglobin in Cardiac Surgery Patients and Its Association with Risk Factors and Biomarkers of Hemolysis

BACKGROUND

Cardiac surgery with cardiopulmonary bypass (CPB) is associated with hemolysis. Yet, there is no easily available and frequently measured marker to monitor this hemolysis. However, carboxyhemoglobin (CO-Hb), formed by the binding of carbon monoxide (a product of heme breakdown) to hemoglobin, may reflect such hemolysis. We hypothesized that CO-Hb might increase after cardiac surgery and show associations with operative risk factors and indirect markers for hemolysis.

METHODS

We conducted a retrospective descriptive cohort study of data from on-pump cardiac surgery patients. We analyzed temporal changes in CO-Hb levels and applied a generalized linear model to assess patient characteristics associated with peak CO-Hb levels. Additionally, we examined their relationship with red blood cell (RBC) transfusion and bilirubin levels.

RESULTS

We studied 38,487 CO-Hb measurements in 1735 patients. CO-Hb levels increased significantly after cardiac surgery, reaching a peak CO-Hb level 2.1 times higher than baseline (P < .001) at a median of 17 hours after the initiation of surgery. Several factors were independently associated with higher peak CO-Hb, including age (P < .001), preoperative respiratory disease (P = .001), New York Heart Association Class IV (P = .019), the number of packed RBC transfused (P < .001), and the duration of CPB (P = .002). Peak CO-Hb levels also significantly correlated with postoperative total bilirubin levels (Rho = 0.27, P < .001).

CONCLUSIONS

CO-Hb may represent a readily obtainable and frequently measured biomarker that has a moderate association with known biomarkers of and risk factors for hemolysis in on-pump cardiac surgery patients. These findings have potential clinical implications and warrant further investigation.

Impact of storage temperature and time before analysis on electrolytes (Na+, K+, Ca2+), lactate, glucose, blood gases (pH, pO2, pCO2), tHb, O2Hb, COHb and MetHb results

OBJECTIVES

The objective of our study is to evaluate the effect of storage temperature and time to analysis on arterial blood gas parameters in order to extend the CLSI recommendations.

METHODS

Stability of 12 parameters (pH, pCO₂, pO₂, Na+, K+, Ca2+, glucose, lactate, hemoglobin, oxyhemoglobin, carboxyhemoglobin, methemoglobin) measured by GEM PREMIER™ 5000 blood gas analyzer was studied at room temperature and at +4 °C (52 patients). The storage times were 30, 45, 60, 90 and 120 min. Stability was evaluated on the difference from baseline, the difference from the analyte-specific measurement uncertainty applied to the baseline value, and the impact of the variation on the clinical interpretation.

RESULTS

At room temperature, all parameters except the lactate remained stable for at least 60 min. A statistically significant difference was observed for pH at T45 and T60 and for pCO2 at T60 without modification of clinical interpretation. For lactate, clinical interpretation was modified from T45 and values were outside the range of acceptability defined by the measurement uncertainty. All parameters except pO2 remained stable for at least 120 min at +4 °C.

CONCLUSIONS

A one-hour transport at room temperature is compatible with the performance of all the analyses studied except lactate. If the delay exceeds 30 min, the sample should be placed at +4 °C for lactate measurement. If the samples are stored in ice, it is important to note that the pO2 cannot be interpreted.

A simple ratiometric fluorescent probe for two-photon imaging of carbon monoxide in living cells and zebrafish

Carbon monoxide (CO) is an important gas signaling molecule and has been widely involved in regulating important life processes. Effective monitoring of CO in living systems is critical. Combined with the accuracy of ratio detection and the advantages of two-photon imaging, a simple ratiometric two-photon fluorescent probe RTFP was rationally designed and synthesized using 7-(diethylamino)-4-hydroxycoumarin as a two-photon fluorophore and allyl carbonate as the reactive unit. Probe RTFP exhibited excellent selectivity and sensitivity towards CO, and was successfully applied to image endogenous CO in living cells and zebrafish.

Quantitative Gas Exchange in Extracorporeal Membrane Oxygenation-A New Device: Accuracy, Approach-based Difficulties, and Caloric Targeting

Measurement of oxygen uptake (VO 2 ) and carbon dioxide removal (VCO 2 ) on membrane lungs (MLs) during extracorporeal membrane oxygenation (ECMO) provides potential for improved and safer therapy. Real-time monitoring of ML function and degradation, calculating caloric needs as well as cardiac output, and weaning algorithms are among the future possibilities. Our study compared the continuous measurement of the standalone Quantum Diagnostics System (QDS) with the published Measuring Energy Expenditure in ECMO patients (MEEP) approach, which calculates sequential VO 2 and VCO 2 values via blood gas analysis and a physiologic gas content model. Thirty-nine datasets were acquired during routine venovenous ECMO intensive care treatment and analyzed. VO 2 was clinically relevant underestimated via the blood-sided measurement of the QDS compared to the MEEP approach (mean difference -42.61 ml/min, limits of agreement [LoA] -2.49/-87.74 ml), which could be explained by the missing dissolved oxygen fraction of the QDS equation. Analysis of VCO 2 showed scattered values with wide limits of agreement (mean difference 54.95 ml/min, LoA 231.26/-121.40 ml/min) partly explainable by a calculation error of the QDS. We described potential confounders of gas-sided measurements in general which need further investigation and recommendations for enhanced devices.

Carboxyhemoglobin as a diagnostic and prognostic biomarker of hemolytic anemias in dogs

BACKGROUND

Endogenous production of carbon monoxide during hemoglobin metabolism leads to the formation of carboxyhemoglobin. Carboxyhemoglobin concentration is abnormally high in humans with hemolytic anemia (HA).

HYPOTHESIS

Measurement of carboxyhemoglobin concentration can discriminate HA from other forms of anemia.

ANIMALS

Twenty-seven dogs with HA (immune-mediated HA, n = 22; microangiopathic HA, n = 5), 27 dogs with non-HA (kidney disease, n = 14; immune-mediated thrombocytopenia, [n = 6]; miscellaneous, n = 7) and 24 nonanemic control dogs.

METHODS

Prospective cohort study. Carboxyhemoglobin quantification, a CBC and biochemistry profile were performed upon admission, and survival to hospital discharge and at 30 days were the measured outcomes. Groups were compared by the Mann-Whitney and Kruskal-Wallis tests. Receiver-operator characteristic (ROC) analyses were used to examine the predictive utility of carboxyhemoglobin for the diagnosis of HA in anemic dogs.

RESULTS

Carboxyhemoglobin (median [interquartile range]) differed between dogs with HA (7.7% [2.5%]) and non-HA (3.6% [1.05]; P < .001) and dogs with HA and nonanemic dogs (3.5% [0.65%]; P < .001). No difference was detected between nonHA and nonanemic dogs. The area under the ROC curve for carboxyhemoglobin as predictor of HA in anemic dogs was 0.997 (95% CI, 0.99-1.00). Three optimal cut-off points were identified, including 5.05%, 4.55% and 4.85%, with corresponding sensitivity/specificity of 92.6%/100%, 100%/92.6% and 96.3%/96.3%, respectively. Neither carboxyhemoglobin nor any of the CBC or chemistry analytes were associated with survival.

CONCLUSIONS AND CLINICAL IMPORTANCE

Carboxyhemoglobin proved an excellent predictor of HA in dogs and might constitute a useful, ancillary tool for diagnosing and monitoring hemolytic anemias.

A new metal-free benzorhodol-based photoluminophore selective for carbon monoxide detection applicable in both in vitro and in vivo bioimaging

A new benzorhodol-based non-fluorescent organic frame (DEB-CO) detects carbon monoxide (CO) selectively through a spirolactam ring-opening mechanism. Herein, the selective off-on fluorogenic behavior of this probe towards CO has been achieved without any assistance of precious and hazardous metals (e.g. Pd²⁺) as additional substrates. Moreover, the red-emissive probe motivated us to apply in situ tracing in mice and living cells. The selective off-on fluorogenic behavior of this probe towards CO originating from CORM-3 in vitro and in vivo with a limit of detection as low as 64.29 nM (for CORM-3) has been observed. Additionally, this probe is capable of sensing toxic carbon monoxide gas. This probe has also been utilized to detect intracellular CO in MCF7 cells (in vitro) and to spot the distribution of CO in mice (in vivo) by acquiring bioimages with the help of confocal microscopy, which indicates that DEB-CO is a smart competent probe for this purpose.

Retrospective evaluation of carboxyhemoglobin and methemoglobin levels in dogs and cats with respiratory disease

OBJECTIVE

To evaluate carboxyhemoglobin (COHb) and methemoglobin (MetHb) levels in dogs and cats with respiratory disease in the ICU.

DESIGN

Retrospective study.

SETTING

University veterinary teaching hospital.

ANIMALS

The ICU census was searched for dogs (n = 466) and cats (n = 97) hospitalized within the ICU between January 2016 and January 2019 in whom blood gas with co-oximetry was performed. Dogs and cats were stratified into those with primary respiratory and nonrespiratory categories; the underlying cause of the disease was also noted. Venous blood gas, co-oximeter, PaO₂ /FiO₂ (PF ratio), physical examination findings, and outcome were recorded.

MEASUREMENTS AND MAIN RESULTS

The median COHb and MetHb in dogs hospitalized in the ICU were 2.6% (0.1%-5.6%) and 1.1% (0.1%-2.9%), respectively. The median COHb and MetHb in cats hospitalized in the ICU were 2.2% (0.1%-5.4%) and 1.0% (0%-2.1%), respectively. Dogs with respiratory disease had a higher COHb than dogs without respiratory disease (median, 2.7% [range, 0.3%-5.0%] vs. 2.5% [0.1%-5.6%]; P = 0.0148). COHb was positively associated with survival in cats (median, 2.2% [range, 0.1%-5.4%] vs. 1.9% [0.1%-3.9%]; P = 0.0433). Both COHb and MetHb were higher in septic dogs than in nonseptic dogs (median COHb, 2.8% [range 0.3%-4.5%] vs. 2.6% [0.1%-5.6%]; P = 0.02 and median MetHb, 1.1% [0.1%-2.9%] vs. 1.1% [0.1%-2.4%]; P = 0.01, respectively).

CONCLUSIONS

There may be a positive association between COHb and respiratory disease in dogs; prospective studies are needed to evaluate this further. No association between COHb and respiratory disease in cats or MetHb and respiratory disease in either species was detected. Additional prospective studies are needed to determine whether COHb and MetHb are biomarkers for sepsis in dogs and whether COHb is an indicator of mortality in cats.

Gases in Sepsis: Novel Mediators and Therapeutic Targets

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

Endogenous carbon monoxide due to hemolytic anemia: A forensic red herring

Carbon monoxide (CO) toxicity associated with exposure to an environmental, exogenous source, is routinely investigated in the field of forensics. Paramedics responded to the home of a 60-year-old woman who complained of persistent nausea, dizziness, and fatigue. Her initial carboxyhemoglobin (COHb) saturation was 25% as measured by paramedics in the field via pulse CO-oximetry (SpCO) and was, 2 hours later, confirmed by hospital laboratory spectrophotometric analysis to be 16% after initial treatment in the emergency department. The clinical presentation of environmental CO exposure and subsequent death notification to the North Carolina Office of the Chief Medical Examiner prompted an extensive investigation into the suspected residential source of CO, which ultimately ruled out all exogenous sources. The medicolegal death investigator later discovered an updated hematology consultation note, which determined the actual source of the CO to be endogenously produced from disease. Herein, we report an unusual fatality involving enhanced endogenous CO production caused by warm autoimmune hemolytic anemia. This unique case report and brief literature review of disease-related elevation of endogenous CO will shed light on this lesser-known phenomenon alerting the forensic community to its potential occurrence and need for consideration when sources of environmental exposure have been exhausted.

Is endogenous carboxyhaemoglobin level a useful biomarker of clinical course and prognosis in COVID-19 patients?

OBJECTIVE

SARS-CoV-2 has caused nearly 4 million confirmed cases of COVID-19 worldwide in the approximately 4 months since it emerged in Wuhan, China in December 2019. Comorbidities increase morbidity and mortality in COVID-19, and many laboratory parameters have been associated with mortality. The aim of the present study was to identify the relationship between endogenous carboxyhaemoglobin (COHb) level and the clinical course and prognosis of COVID-19.

METHODS

The study included 48 non-smokers or ex-smokers aged 18 years or older who presented to the emergency department, were diagnosed with COVID-19 by real-time PCR analysis of nasopharyngeal swab sample and were treated in the pulmonary diseases ward of the Atatürk University hospital after 24 March 2020 and 15 April 2020. The patients' laboratory parameters and demographic data were analysed retrospectively.

RESULTS

Prothrombin time and C-reactive protein (CRP), troponin-I, and D-dimer levels decreased in COVID-19 patients during follow-up (P = .024, P = .001, P = .001, P = .001), while PaO₂ /FiO₂ ratio and COHb increased (P = .002, P = .001). COHb level at admission was significantly lower in patients who developed macrophage activation syndrome (MAS), acute respiratory distress syndrome (ARDS), and those who died compared with the other patients (P = .002, P = .001). COHb level on day 5 of treatment was significantly higher in patients with ARDS and patients who died (P = .001, P = .001). Significant correlations were detected between COHb level and CRP (r=-0.425, P = .001), ferritin (r = -.395, P = .001) and PaO₂ /FiO₂ ratio (r = .431, P = .001).

CONCLUSIONS

COHb level may be an easily accessible biomarker that guides early follow-up and treatment planning to avoid ARDS, MAS and mortality in COVID-19.

Silent Hypoxemia in Patients with COVID-19 Pneumonia: A Review

During the coronavirus disease 2019 (COVID-19) pandemic due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, patients presented with COVID-19 pneumonia of varying severity. The phenomenon of severe hypoxemia without signs of respiratory distress is also known as silent or hidden hypoxemia. Although silent hypoxemia is not unique to pneumonia due to SARS-CoV-2 infection, this phenomenon is now recognized to be associated with severe COVID-19 pneumonia. Proper management of critically ill patients is the key to reducing mortality. Herein, we summarize the possible and rare factors contributing to silent hypoxemia in patients with COVID-19. Microvascular thrombosis causes dead space ventilation in the lungs, and the flow of pulmonary capillaries is reduced, which leads to an imbalance in the V/Q ratio. The dissociation curve of oxyhemoglobin shifts to the left and limits the release of oxygen to the tissue. SARS-CoV-2 interferes with the synthesis of hemoglobin and reduces the ability to carry oxygen. The accumulation of endogenous carbon monoxide and carboxyhemoglobin will reduce the total oxygen carrying capacity and interfere with pulse oxygen saturation readings. There are also some non-specific factors that cause the difference between pulse oximetry and oxygen partial pressure. We propose some potentially more effective clinical alternatives and recommendations for optimizing the clinical management processes of patients with COVID-19. This review aims to describe the prevalence of silent hypoxemia in COVID-19 pneumonia, to provide an update on what is known of the pathophysiology, and to highlight the importance of diagnosing silent hypoxemia in patients with COVID-19 pneumonia.

Sensitive and effective imaging of carbon monoxide in living systems with a near-infrared fluorescent probe

CO, a gas molecule that is harmful to living organisms, has a high affinity with hemoglobin, which will cause severe hypoxia. However, in recent years, researchers have discovered that endogenous CO, similar to NO, is one of the messenger molecules, which has a certain regulatory effect in many physiological and pathological processes in the respiratory system, cardiovascular system, and nervous system. Therefore, it is urgent to explore an effective method to monitor the role of CO under physiological and pathological conditions. Herein, we designed and synthesized a near-infrared small-molecule fluorescent probe for the detection of CO in living cells. In this design, a two-site BODIPY dye was introduced as the fluorophore, and the allyl chloroformate part as the CO reactive group. The probe displays excellent sensitivity, selectivity, and a good linear relationship to CO. Furthermore, it shows good biocompatibility and low cytotoxicity. This probe has been successfully applied to the detection of CO in a variety of cells. The developed fluorescent probe can serve as a potential molecular imaging tool for in vivo imaging and detection of CO.

Behavior of carbon monoxide, nitrogen oxides, and ozone in a vehicle cabin with a passenger

Drivers and passengers are exposed to high concentrations of air pollutants while driving. While there are many studies to assess exposure to air pollutants penetrating into a vehicle cabin, little is known about how individual gas pollutants are behaving (e.g. accumulating, depositing, reacting etc.) in the cabin. This study investigated the characteristic behavior of CO, NO, NO2 and O3 in a vehicle cabin in the presence of a driver with static, pseudo dynamic and dynamic tests. We found in our experiments that CO and NO concentrations increased while O3 and NO2 concentrations decreased rapidly when cabin air was recirculated. A kinetic model, which contains 20 chemical reactions, could predict the static test results well. CO and NO accumulations in the cabin were due to exhalation from the driver and conversion of NO2 to NO upon deposition to surfaces may also play a role. Pseudo dynamic and dynamic test results showed similar results. During the fresh air mode CO, NO, and NO2 followed similar trends between the inside and outside of the cabin, while in cabin O3 concentrations were lower compared to outside concentrations due to reactions with the human and surface deposition. The Cabin Air Quality Index approached 0.8 and 0.4 for O3 during pseudo dynamic and dynamic tests, respectively. Accumulation of NO in the cabin was not obvious during the dynamic test due to a large variation of outside NO concentrations. We encourage auto manufacturers to develop control algorithms and devices to reduce a passenger's exposure to gaseous pollutants in vehicle cabins.

Endogenous Carbon Monoxide Production and Diffusing Capacity of the Lung for Carbon Monoxide in Sepsis-Induced Acute Respiratory Distress Syndrome

Low-dose inhaled carbon monoxide is a novel therapeutic under investigation in acute respiratory distress syndrome. The Coburn-Forster-Kane equation is a well-validated model of carbon monoxide uptake that can accurately predict carboxyhemoglobin levels to ensure safe administration of low-dose inhaled carbon monoxide in patients with acute respiratory distress syndrome. Using data from a Phase I trial of low-dose inhaled carbon monoxide, we performed a post hoc analysis to determine if the Coburn-Forster-Kane equation could be used to assess the diffusing capacity of the lung for carbon monoxide and endogenous carbon monoxide production in patients with sepsis-induced acute respiratory distress syndrome. Diffusing capacity of the lung for carbon monoxide was substantially reduced and correlated with Pao₂/Fio₂ and Sequential Organ Failure Assessment score. Endogenous carbon monoxide production was markedly elevated and was significantly associated with Lung Injury Score in sepsis-induced acute respiratory distress syndrome patients. Our data suggest that the Coburn-Forster-Kane equation can be used to estimate diffusing capacity of the lung for carbon monoxide and endogenous carbon monoxide production in mechanically ventilated patients. We found that increased endogenous carbon monoxide production and reduced diffusing capacity of the lung for carbon monoxide correlate with clinical endpoints associated with outcomes in patients with sepsis-induced acute respiratory distress syndrome.

Association of exhaled carbon monoxide with risk of cardio-cerebral-vascular disease in the China Kadoorie Biobank cohort study

Exhaled carbon monoxide (COex) level has been proposed as a noninvasive and easily-obtainable cardiovascular risk marker, however, with limited prospective evidence, and its association with stroke risk has been rarely explored. Measurements of COex were performed during 2004-2008 baseline examinations in the China Kadoorie Biobank study among 512,891 adults aged 30-79 years from 10 diverse study areas. After excluding participants with baseline cardiopulmonary diseases, stroke and cancer, 178,485 men and 267,202 women remained. Cox regression yielded hazard ratios (HRs) and 95% confidence intervals (CIs) for risk of cardio-cerebral-vascular disease (CCVD) associated with COex levels, with sequential addition of adjustment for proxy variables for CO exposure, including study area indexing ambient CO variations at large, and smoking and solid fuel use, apart from adjusting for traditional cardiovascular risk factors. During 7-year follow-up, we documented 1744 and 1430 major coronary events (myocardial infarction plus fatal ischemic heart disease), 8849 and 10,922 ischemic strokes, and 2492 and 2363 hemorrhagic strokes among men and women, respectively. The HRs with 95% CIs comparing the highest with lowest COex quintile were 2.15 [1.72, 2.69] for major coronary events, 1.65 [1.50, 1.80] for ischemic stroke, and 1.35 [1.13, 1.61] for hemorrhagic stroke among men, while among women higher associated risk was only observed for major coronary events (1.64 [1.35, 2.00]) and ischemic stroke (1.87 [1.73, 2.01]). The elevated risks were consistent when COex level was over 3 ppm. However, these associations were all attenuated until null by sequential addition of stratification by study areas, and adjustments of smoking and solid fuel use. Nevertheless, the association with ischemic stroke was maintained among the subgroup of male smokers even with adjustment for the depth and amount of cigarette smoking (HR [95% CI]: 1.37 [1.06, 1.77]), while a negative association with hemorrhagic stroke also appeared within this subgroup. Higher COex level (over 3 ppm) was associated with elevated risk of ischemic CCVD, but not independently of CO exposure. Our finding suggests that, though not an independent risk factor, COex could potentially provide a cost-effective biomarker for ischemic cardio-cerebral-vascular risk, given that CO exposure is ubiquitous.

Impact of breath sampling on exhaled carbon monoxide

The influence of breath sampling on exhaled carbon monoxide (eCO) and related pulmonary gas exchange parameters is investigated in a study with 32 healthy non-smokers. Mid-infrared tunable diode laser absorption spectroscopy and well-controlled online sampling is used to precisely measure mouth- and nose-exhaled CO expirograms at exhalation flow rates (EFRs) of 250, 120 and 60 ml s^-1, and for 10 s of breath-holding followed by exhalation at 120 ml s^-1. A trumpet model with axial diffusion is employed to fit simulated exhalation profiles to the experimental expirograms, which provides equilibrium airway and alveolar CO concentrations and the average lung diffusing capacity in addition to end-tidal concentrations. For all breathing maneuvers, excellent agreement is found between mouth- and nose-exhaled end-tidal CO (ETCO), and the individual values for ETCO and alveolar diffusing capacity are consistent across maneuvers. The eCO parameters clearly show a dependence on EFR, where the lung diffusing capacity increases with EFR, while ETCO slightly decreases. End-tidal CO is largely independent of ambient air CO and alveolar diffusing capacity. While airway CO is slightly higher than, and correlates strongly with, ambient air CO, and there is a weak correlation with ETCO, the results point to negligible endogenous airway CO production in healthy subjects. An EFR of around 120 ml s^-1 can be recommended for clinical eCO measurements. The employed method provides means to measure variations in endogenous CO, which can improve the interpretation of exhaled CO concentrations and the diagnostic value of eCO tests in clinical studies. Clinical trial registration number: 2017/306-31.

Carbon monoxide poisoning

Carbon monoxide (CO) is the leading cause of poisoning deaths in many countries, including Japan. Annually, CO poisoning claims about 2000-5000 lives in Japan, which is over half of the total number of poisoning deaths. This paper discusses the physicochemical properties of CO and the toxicological evaluation of CO poisoning.

Styrene-maleic acid copolymer-encapsulated carbon monoxide releasing molecule-2 (SMA/CORM-2) suppresses proliferation, migration and invasion of colorectal cancer cells in vitro and in vivo

Although increasing evidence have confirmed that carbon monoxide release molecule-2(CORM-2) plays an active role in the treatment of inflammation and tumors, poor aqueous solubility and short CO-release duration restrict its extensive application. Our previous work synthesized styrene-maleic acid copolymer-encapsulated CORM-2 (SMA/CORM-2) to overcome above-mentioned deficiencies and demonstrated satisfactory effects in colitis. This study is to investigate the function of SMA/CORM-2 on colorectal cancer proliferation and metastasis. CCK-8 experiment is used to clarify the half maximal inhibitory concentration (IC50) of SMA/CORM-2 and to detect cell proliferation. Transwell assay coated with or without matrigel was to detect cell invasion and migration. Western blot was used to detect β-catenin, AKT, p-AKT, VEGF, MMP-2 and MMP-9 proteins. At last, nude mice xenograft was used to further investigate the anti-tumor effect of SMA/CORM-2 in vivo. After SW480 and C26 cells were treated with 0.5 mg/ml SMA/CORM-2, CRC cells proliferation, migration and invasion were inhibited. In vivo, SMA/CORM-2 treatment remarkably suppressed tumor growth and lung metastasis in nude mice. Furthermore, the expression of β-catenin, p-AKT, VEGF, MMP-2 and MMP-9 proteins could be down-regulated after SMA/CORM-2 treatment. SMA/CORM-2 exerted both in vitro and in vivo anti-proliferation and anti-metastatic effects, which may yield a novel therapeutic strategy for CRC.

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.

A cell membrane-anchored fluorescent probe for monitoring carbon monoxide release from living cells

Carbon monoxide (CO) acts as an important gasotransmitter in delivering intramolecular and intermolecular signals to regulate a variety of physiological processes. This lipid-soluble gas can freely pass through the cell membrane and then diffuse to adjacent cells acting as a messenger. Although many fluorescent probes have been reported to detect intracellular CO, it is still a challenge to visualize the release behavior of endogenous CO. The main obstacle is the lack of a probe that can anchor onto the cell membrane while having the ability to image CO in real time. In this work, by grafting a polar head onto a long and linear hydrophobic Nile Red molecule, a cell membrane-anchored fluorophore ANR was developed. This design strategy of a cell membrane-anchored probe is simpler than the traditional one of using a long hydrophobic alkyl chain as a membrane-anchoring group, and endows the probe with better water solubility. ANR could rapidly bind to the cell membrane (within 1 min) and displayed a long retention time. ANR was then converted to a CO-responsive fluorescent probe (ANRP) by complexation with palladium based on a metal palladium-catalyzed reaction. ANRP exhibited a fast response to CO with a 25-fold fluorescence enhancement in vitro. The detection limit was calculated to be 0.23 μM, indicating that ANRP is sensitive enough to image endogenous CO. Notably, ANRP showed excellent cell membrane-anchoring ability. With ANRP, the release of CO from HepG2 cells under LPS- and heme-stimulated conditions was visualized and the cell self-protection effect during a drug-induced hepatotoxicity process was also studied. Moreover, ANRP was successfully applied to the detection of intracellular CO in several cell lines and tissues, and the results demonstrated that the liver is the main organ for CO production, and that cancer cells release more CO from their cells than normal cells. ANRP is the first membrane-anchored CO fluorescent probe that has the ability to reveal the relationship between CO release and diseases. It also has prospects for the studying of intercellular signaling functions of CO.

Elevated blood carboxyhemoglobin levels as an early predictor of phototherapy requirement in moderate and late preterm infants

Objective: Preterm infants are prone to increased bilirubin burden and display adverse outcomes if left unmonitored; therefore, predicting an increased bilirubin production is of paramount importance.Methods: We aimed to evaluate carboxyhemoglobin (COHb) levels in moderate (GA: 32^0/7-33^6/7) and late preterm (GA: 34^0/7-36^6/7) infants to assess whether this molecule could be used as an early predictor of phototherapy requirement.Results: A total of 221 infants were enrolled in the study. On admission, carboxyhemoglobin levels of infants who received phototherapy were significantly higher than that of infants who did not require this treatment, and this difference persisted in the consecutive hours (median (min-max): 1.2% (0.3-1.7) versus 0.8% (0.4-1.1); p < .001). The initial and consecutive COHb levels showed positive correlation (r = 0.77, p < .001). In the post-hoc analysis, direct antiglobulin test positivity significantly affected phototherapy requirement (p < .001). Receiver operating characteristics analysis showed that a COHb level of ≥0.95% was found to have a sensitivity of 90% and a specificity of 88%. Multinomial logistic regression analysis demonstrated that high COHb levels on admission significantly increased the likelihood of phototherapy requirement when adjusted for covariants (adjusted odds ratio: 2.2; 95% confidence interval: 1.4-3.5; p < .001).Conclusion: Carboxyhemoglobin measurement can be simply used to predict preterm infants who will require phototherapy.

Modeling Pulmonary Gas Exchange and Single-Exhalation Profiles of Carbon Monoxide

Exhaled breath carbon monoxide (eCO) is a candidate biomarker for non-invasive assessment of oxidative stress and respiratory diseases. Standard end-tidal CO analysis, however, cannot distinguish, whether eCO reflects endogenous CO production, lung diffusion properties or exogenous sources, and is unable to resolve a potential airway contribution. Coupling real-time breath gas analysis to pulmonary gas exchange modeling holds promise to improve the diagnostic value of eCO. A trumpet model with axial diffusion (TMAD) is used to simulate the dynamics of CO gas exchange in the respiratory system and corresponding eCO concentrations for the first time. The mass balance equation is numerically solved employing a computationally inexpensive routine implementing the method of lines, which provides the distribution of CO in the respiratory tract during inhalation, breath-holding, and exhalation with 1 mm spatial and 0.01 s temporal resolution. Initial estimates of the main TMAD parameters, the maximum CO fluxes and diffusing capacities in alveoli and airways, are obtained using healthy population tissue, blood and anatomical data. To verify the model, mouth-exhaled expirograms from two healthy subjects, measured with a novel, home-built laser-based CO sensor, are compared to single-exhalation profiles simulated using actual breath sampling data, such as exhalation flow rate (EFR) and volume. A very good agreement is obtained in exhalation phases I and III for EFRs between 55 and 220 ml/s and after 10 and 20 s of breath-holding, yielding a unique set of TMAD parameters. The results confirm the recently observed EFR dependence of CO expirograms and suggest that measured end-tidal eCO is always lower than alveolar and capillary CO. Breath-holding allows the observation of close-to-alveolar CO concentrations and increases the sensitivity to the airway TMAD parameters in exhalation phase I. A parametric simulation study shows that a small increase in airway flux can be distinguished from an increase in alveolar flux, and that slight changes in alveolar flux and diffusing capacity have a significantly different effect on phase III of the eCO profiles.

Gaseous Signaling Molecules in Cardiovascular Function: From Mechanisms to Clinical Translation

Carbon monoxide (CO), hydrogen sulfide (H₂S), and nitric oxide (NO) constitute endogenous gaseous molecules produced by specific enzymes. These gases are chemically simple, but exert multiple effects and act through shared molecular targets to control both physiology and pathophysiology in the cardiovascular system (CVS). The gases act via direct and/or indirect interactions with each other in proteins such as heme-containing enzymes, the mitochondrial respiratory complex, and ion channels, among others. Studies of the major impacts of CO, H₂S, and NO on the CVS have revealed their involvement in controlling blood pressure and in reducing cardiac reperfusion injuries, although their functional roles are not limited to these conditions. In this review, the basic aspects of CO, H₂S, and NO, including their production and effects on enzymes, mitochondrial respiration and biogenesis, and ion channels are briefly addressed to provide insight into their biology with respect to the CVS. Finally, potential therapeutic applications of CO, H₂S, and NO with the CVS are addressed, based on the use of exogenous donors and different types of delivery systems.

Use of carboxyhemoglobin as a biomarker of environmental CO exposure: critical evaluation of the literature

Carbon monoxide (CO) poisoning is the primary cause for access to emergency department (ED) services for more than 50,000 persons in Europe and the USA every year. CO poisoning diagnosis is based on multiple factors and is usually confirmed by high carboxyhemoglobin (COHb) levels in the blood. We conducted a systematic evaluation of literature to investigate the usefulness of COHb as a biomarker of environmental CO exposure. We conducted an electronic search in Medline, Embase, and the Cochrane Library databases. We selected studies reporting high or low environmental CO concentrations, as well as COHb levels in exposed subjects presenting in ED or staying at home. We included 19 studies, but only 7 studies reported environmental CO concentration and proved a correlation between COHb and CO exposure in healthy and non-smoker subjects only. However, confounding factors were often incompletely assessed. The main symptoms reported were headache, nausea, vertigo and vomiting. COHb data stored in healthcare databases were used in six studies and provided useful information about symptoms, CO sources and patient characteristics. Most studies were classified at risk of bias. This review indicates that COHb is the most commonly used biomarker to assess CO exposure and seems to be useful. Further studies are needed to establish the reliability of COHb as a biomarker and/or explore other possible biomarkers. Surveillance systems of the general population, correlated with geographical locations and other confounding factors, could be important for CO exposure monitoring and the development of focused prevention programs.

ICL-based TDLAS sensor for real-time breath gas analysis of carbon monoxide isotopes

We present a compact sensor for carbon monoxide (CO) in air and exhaled breath based on a room temperature interband cascade laser (ICL) operating at 4.69 µm, a low-volume circular multipass cell and wavelength modulation absorption spectroscopy. A fringe-limited (1σ) sensitivity of 6.5 × 10^-8 cm^-1Hz^-1/2 and a detection limit of 9 ± 5 ppbv at 0.07 s acquisition time are achieved, which constitutes a 25-fold improvement compared to direct absorption spectroscopy. Integration over 10 s increases the precision to 0.6 ppbv. The setup also allows measuring the stable isotope ¹³CO in breath. We demonstrate quantification of indoor air CO and real-time detection of CO expirograms from healthy non-smokers and a healthy smoker before and after smoking. Isotope ratio analysis indicates depletion of ¹³CO in breath compared to natural abundance.

Structural isomerism of Ru(ii)-carbonyl complexes: synthesis, characterization and their antitrypanosomal activities

New complexes with the formula [RuCl(CO)(dppb)(N–N)]PF₆ were prepared by varying the CO position as well as the diimine ligand.

Relationship between obstructive sleep apnea and endogenous carbon monoxide

Endogenous carbon monoxide (CO) levels are recognized as a surrogate marker for activity of heme oxygenase-1, which is induced by various factors, including hypoxia and oxidative stress. Few reports have evaluated endogenous CO in patients with obstructive sleep apnea (OSA). Whether OSA more greatly affects exhaled or blood CO is not known. Sixty-nine patients with suspected OSA were prospectively included in this study. Exhaled and blood CO were evaluated at night and morning. Blood and exhaled CO levels were well correlated both at night and morning (r = 0.52, P < 0.0001 and r = 0.61, P < 0.0001, respectively). Although exhaled CO levels both at night and morning significantly correlated with total sleep time with arterial oxygen saturation < 90% (ρ = 0.41, P = 0.0005 and ρ = 0.27, P = 0.024, respectively), blood CO levels did not correlate with any sleep parameter. Seventeen patients with an apnea and hypopnea index (AHI) < 15 (control group) were compared with 52 patients with AHI ≥ 15 (OSA group). Exhaled CO levels at night in the OSA group were significantly higher than in the control group (3.64 ± 1.2 vs. 2.99 ± 0.70 ppm, P < 0.05). Exhaled CO levels at night decreased after 3 mo of continuous positive airway pressure (CPAP) therapy in OSA patients (n = 36; P = 0.016) to become nearly the same level as in the control group (P = 0.21). Blood CO levels did not significantly change after CPAP therapy. Exhaled CO was positively related to hypoxia during sleep in OSA patients, but blood CO was not. Exhaled CO might better correlate with oxidative stress associated with OSA than blood CO.

NEW & NOTEWORTHY

Endogenous carbon monoxide (CO) levels are recognized to be a surrogate marker of oxidative stress. No study has evaluated both exhaled and blood CO at the same time in obstructive sleep apnea (OSA) patients. Here we provide evidence that exhaled CO levels positively correlated with hypoxia during sleep in OSA patients, but blood CO levels did not, and that continuous positive airway pressure therapy significantly decreased exhaled CO levels in the OSA group, but did not significantly affect blood CO.

Left Ventricular Assist Device-Associated Carbon Monoxide and Iron-Enhanced Hypercoagulation: Impact of Concurrent Disease

Left ventricular assist device (LVAD) therapy is associated with thrombophilia despite anticoagulation. Of interest, LVAD patients have increased carboxyhemoglobin, a measure of upregulated heme oxygenase (Hmox) activity that releases carbon monoxide (CO) and iron. Given that CO and iron enhance plasmatic coagulation, we determined if LVAD patients had hypercoagulability and decreased fibrinolytic vulnerability with measurable CO and iron-mediated effects. Blood samples were obtained a month or more after implantation of the LVAD. Thrombelastographic methods to assess coagulation kinetics, fibrinolytic kinetics, formation of carboxyhemefibrinogen, and iron-mediated enhancement of clot growth were utilized. Coagulation and fibrinolytic parameter normal individual (n = 30) plasma values were determined. Sixteen LVAD patients were studied. CO and iron enhancement of coagulation were observed in the majority of LVAD patients, contributing to hypercoagulation. However, most patients demonstrated abnormally increased rates of clot lysis. Critically, hemolysis as assessed by circulating lactate dehydrogenase activity was small in this cohort, and only four patients without comorbid states (e.g., obesity, diabetes, sleep apnea) were hypercoagulable with evidence of Hmox upregulation. However, seven patients with comorbidities were hypercoagulable with Hmox upregulation. Future investigation of CO and iron-related thrombophilia and comorbid disease is warranted to define its role in LVAD-related thrombosis.

Association of Exhaled Carbon Monoxide With Stroke Incidence and Subclinical Vascular Brain Injury: Framingham Heart Study

BACKGROUND AND PURPOSE

Exhaled carbon monoxide (CO) is associated with cardiometabolic traits, subclinical atherosclerosis, and cardiovascular disease, but its specific relations with stroke are unexplored. We related exhaled CO to magnetic resonance imaging measures of subclinical cerebrovascular disease cross-sectionally and to incident stroke/transient ischemic attack prospectively in the Framingham Offspring study.

METHODS

We measured exhaled CO in 3313 participants (age 59±10 years; 53% women), and brain magnetic resonance imaging was available in 1982 individuals (age 58±10 years; 54% women). Participants were analyzed according to tertiles of exhaled CO concentration.

RESULTS

In age- and sex-adjusted models, the highest tertile of exhaled CO was associated with lower total cerebral brain volumes, higher white-matter hyperintensity volumes, and greater prevalence of silent cerebral infarcts (P<0.05 for all). The results for total cerebral brain volume and white-matter hyperintensity volume were consistent after removing smokers from the sample, and the association with white-matter hyperintensity volume persisted after multivariable adjustment (P=0.04). In prospective analyses (mean follow-up 12.9 years), higher exhaled CO was associated with 67% (second tertile) and 97% (top tertile) increased incidence of stroke/transient ischemic attack relative to the first tertile that served as referent (P<0.01 for both). These results were consistent in nonsmokers and were partially attenuated upon adjustment for vascular risk factors.

CONCLUSIONS

In this large, community-based sample of individuals without clinical stroke/transient ischemic attack at baseline, higher exhaled CO was associated with a greater burden of subclinical cerebrovascular disease cross-sectionally and with increased risk of stroke/transient ischemic attack prospectively. Further investigation is necessary to explore the biological mechanisms linking elevated CO with stroke.

Expired-air carbon monoxide as a predictor of 16-year risk of all-cause, cardiovascular and cancer mortality

BACKGROUND

Measurement of expired-air carbon monoxide (EACO) is commonly used to ascertain non-smoking status, although it can also reflect exposures not related to smoking. Our aim was to assess 16-year mortality according to EACO measured at baseline, in a general population.

METHODS

Our analysis was based on the Third French MONICA population survey (1994-1997). Causes of death were obtained 16 years after inclusion, and assessment of determinants of mortality was based on Cox modeling.

RESULTS

EACO was measured in 2232 apparently healthy participants aged 35-64. During follow-up, 195 deaths occurred (19% were due to cardio-vascular (CV) causes and 49% to cancer). At baseline, the mean EACO was 11.8 (±7.4)ppm, 4.6 (±2.5)ppm, 4.3 (±2.2)ppm for current, former and never smokers, respectively (P<0.001). After adjustment for main mortality risk factors and smoking, the hazard ratio (HR) for total mortality was 1.03[95% confidence interval: 1.01-1.06] per 1-unit increase in EACO, and it was 1.04[1.01-1.07] for cancer mortality. Adjusted HR for CV mortality was 1.05[1.01-1.10] but did not remain significant after additional adjustment for smoking (0.98[0.91-1.04]). Interactions between EACO and smoking were not significant.

CONCLUSIONS

In a general population, baseline EACO is an independent predictor of 16-year all-cause and cancer mortality, after adjustment for confounders including smoking. Given that the effect of EACO is similar among smokers and non-smokers, EACO is probably not solely related to smoking but could also be a marker of inhaled ambient carbon monoxide and/or endogenous production. Besides, smoking better predicts CV mortality than EACO.

Hemodialysis patients have plasmatic hypercoagulability and decreased fibrinolytic vulnerability: role of carbon monoxide

Chronic hemodialysis is associated with significant thrombophilia. Of interest, hemodialysis patients have increased carboxyhemoglobin (COHb) and exhaled carbon monoxide (CO), signs of upregulated heme oxygenase (Hmox) activity. Given that CO enhances plasmatic coagulation, we determined whether patients requiring chronic hemodialysis had an increase in endogenous CO, plasmatic hypercoagulability and decreased fibrinolytic vulnerability. Carbon monoxide was determined by noninvasive pulse oximetry measurement of COHb. Blood samples were obtained just before hemodialysis. Thrombelastographic methods to assess plasma coagulation kinetics, fibrinolytic kinetics, and formation of carboxyhemefibrinogen (COHF) were used. Hemodialysis patients (n = 45) had abnormally increased COHb concentrations of 2.2 ± 1.9%, indicative of Hmox upregulation. Coagulation and fibrinolytic parameter normal values were determined with normal individual (n = 30) plasma. Thirty-seven patients of the hemodialysis cohort had COHF formation (82.2%, [67.9%-92.0%]; mean, [95% confidence interval]), and many of this group of patients had abnormally great velocity of clot growth (73.3%, [58.1%-85.4%]) and strength (75.6%, [60.5%-87.1%]). Furthermore, over half of COHF positive patients had a hypofibrinolytic state, evidenced by an abnormally prolonged time to maximum rate of lysis (53.3%, [37.9%-68.6%]) and clot lysis time (64.4%, [48.8%-78.1%]). Carbon monoxide enhanced coagulation and diminished fibrinolytic vulnerability in hemodialysis patients. Future investigation of hemodialysis, CO-related thrombophilia is warranted.

Effect of carbon monoxide on gene expression in cerebrocortical astrocytes: Validation of reference genes for quantitative real-time PCR

Quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR) is a widely used technique to characterize changes in gene expression in complex cellular and tissue processes, such as cytoprotection or inflammation. The accurate assessment of changes in gene expression depends on the selection of adequate internal reference gene(s). Carbon monoxide (CO) affects several metabolic pathways and de novo protein synthesis is crucial in the cellular responses to this gasotransmitter. Herein a selection of commonly used reference genes was analyzed to identify the most suitable internal control genes to evaluate the effect of CO on gene expression in cultured cerebrocortical astrocytes. The cells were exposed to CO by treatment with CORM-A1 (CO releasing molecule A1) and four different algorithms (geNorm, NormFinder, Delta Ct and BestKeeper) were applied to evaluate the stability of eight putative reference genes. Our results indicate that Gapdh (glyceraldehyde-3-phosphate dehydrogenase) together with Ppia (peptidylpropyl isomerase A) is the most suitable gene pair for normalization of qRT-PCR results under the experimental conditions used. Pgk1 (phosphoglycerate kinase 1), Hprt1 (hypoxanthine guanine phosphoribosyl transferase I), Sdha (Succinate Dehydrogenase Complex, Subunit A), Tbp (TATA box binding protein), Actg1 (actin gamma 1) and Rn18s (18S rRNA) genes presented less stable expression profiles in cultured cortical astrocytes exposed to CORM-A1 for up to 60 min. For validation, we analyzed the effect of CO on the expression of Bdnf and bcl-2. Different results were obtained, depending on the reference genes used. A significant increase in the expression of both genes was found when the results were normalized with Gapdh and Ppia, in contrast with the results obtained when the other genes were used as reference. These findings highlight the need for a proper and accurate selection of the reference genes used in the quantification of qRT-PCR results in studies on the effect of CO in gene expression.

Noninvasive effects measurements for air pollution human studies: methods, analysis, and implications

Human exposure studies, compared with cell and animal models, are heavily relied upon to study the associations between health effects in humans and air pollutant inhalation. Human studies vary in exposure methodology, with some work conducted in controlled settings, whereas other studies are conducted in ambient environments. Human studies can also vary in the health metrics explored, as there exists a myriad of health effect end points commonly measured. In this review, we compiled mini reviews of the most commonly used noninvasive health effect end points that are suitable for panel studies of air pollution, broken into cardiovascular end points, respiratory end points, and biomarkers of effect from biological specimens. Pertinent information regarding each health end point and the suggested methods for mobile collection in the field are assessed. In addition, the clinical implications for each health end point are summarized, along with the factors identified that can modify each measurement. Finally, the important research findings regarding each health end point and air pollutant exposures were reviewed. It appeared that most of the adverse health effects end points explored were found to positively correlate with pollutant levels, although differences in study design, pollutants measured, and study population were found to influence the magnitude of these effects. Thus, this review is intended to act as a guide for researchers interested in conducting human exposure studies of air pollutants while in the field, although there can be a wider application for using these end points in many epidemiological study designs.

Point-of-care end-tidal carbon monoxide reflects severity of hemolysis in sickle cell anemia

Carbon monoxide (CO) production from heme catabolism is increased with hemolysis. A portable end-tidal CO (ETCO) monitor was used to analyze breath samples in 16 children with sickle cell anemia (SCA, 5-14 years). Median (range) ETCO for SCA was 4.35 ppm (1.8-9.7) versus 0.80 ppm (0.2-2.3) for controls (P < 0.001). ETCOc >2.1 ppm provided sensitivity and specificity of 93.8% (69.8-99.8%) for detecting SCA. ETCO correlated with reticulocytosis (P = 0.015) and bilirubin (P = 0.009), and was 32% lower in children receiving hydroxyurea (P = 0.09). Point-of-care ETCO analysis may prove useful for non-invasive monitoring of hemolysis and as a screening test for SCA.

The role of carboxyhemoglobin measured with CO-oximetry in the detection of hemolysis in newborns with ABO alloimmunization

OBJECTIVES

To evaluate carboxyhemoglobin (COHb) values measured with a CO-oximeter (Roche-cobas b 221) in jaundiced newborns with or without hemolysis and healthy controls in order to assess whether COHb measurement determined with a CO-oximeter could be used as an indicator of hemolysis in newborns with ABO alloimmunization.

METHODS

A total of 86 term newborn infants were prospectively studied. The study cohort consisted of three subgroups: 18 infants with ABO HDN, 21 infants with hyperbilirubinemia without hemolytic disease who required phototherapy, and 47 healthy controls. The COHb, bilirubin, and Hb levels were measured.

RESULTS

The three subgroups did not differ significantly with respect to birth weight, gestational age, gender, Apgar score, or mode of delivery. The ABO HDN infants had significantly higher COHb values than the healthy controls (median 2.4% versus 1.3%, p < 0.0005) and the group with hyperbilirubinemia without hemolytic disease (median 2.4% versus 1.3%, p < 0.0005), although the infants with hyperbilirubinemia without hemolytic disease did not have significantly higher COHb values compared with the healthy controls. The cut-off value of 1.7% COHb had 72% sensitivity and 97% specificity for confirming hemolysis in ABO alloimmunization.

CONCLUSIONS

Our data show that COHb values determined with CO-oximeters are higher in newborns with hemolysis than in those without hemolysis. COHb measured with CO-oximeters could be used to confirm hemolysis in infants with ABO alloimmunization.

Normal values of exhaled carbon monoxide in healthy subjects: comparison between two methods of assessment

Background

In a previous study, exhaled carbon monoxide (eCO) has been assessed in healthy non-smokers with a photo acoustic spectrometer Brüel&Kjær 1312. Unexpectedly, values were higher than those reported in literature, which were mostly obtained with electrochemical analysers. This study was aimed to compare eCO values obtained with Brüel&Kjær 1312 and PiCO + Smokerlyzer, a largely utilized electrochemical analyser.

Methods

Thirty-four healthy subjects, 15 non-smokers and 19 smokers, underwent eCO assessment with Brüel&Kjær 1312 and PiCO + Smokerlyzer during a prolonged expiration (15 seconds). Brüel&Kjær 1312 assessed CO concentration 7 and 12 seconds after the beginning of expiration and displayed the mean value. PiCO + Smokerlyzer was utilized according to the manufacturer’s recommendations. In vitro, the two devices were tested with standard concentrations of CO in nitrogen (5, 9.9, 20, and 50 ppm), and the time needed by PiCO + Smokerlyzer readings to stabilize was assessed at different gas flows.

Results

Both Brüel&Kjær 1312 and PiCO + Smokerlyzer presented very good internal consistency. The values provided were strictly correlated, but at low test concentrations, the Brüel&Kjær 1312 readings were greater than the PiCO + Smokerlyzer, and vice versa. PiCO + Smokerlyzer overestimated the CO standard concentrations at 5 and 9.9 ppm by 20%, while Brüel&Kjær 1312 measures were correct. PiCO + Smokerlyzer readings stabilized in 12 seconds during in vitro tests and in 15 seconds during in vivo measurements, suggesting that the values displayed corresponded to the initial phase of expiration.

Conclusions

Differences between Brüel&Kjær 1312 and PiCO + Smokerlyzer may be explained because Brüel&Kjær 1312 measured CO levels in the middle and at the end of expiration while PiCO + Smokerlyzer assessed them in the initial part of expiration.

Association of exhaled carbon monoxide with subclinical cardiovascular disease and their conjoint impact on the incidence of cardiovascular outcomes

AIMS

Whereas endogenous carbon monoxide (CO) is cytoprotective at physiologic levels, excess CO concentrations are associated with cardiometabolic risk and may represent an important marker of progression from subclinical to clinical cardiovascular disease (CVD).

METHODS AND RESULTS

In 1926 participants of the Framingham Offspring Study (aged 57 ± 10 years, 46% women), we investigated the relationship of exhaled CO, a surrogate of blood CO concentration, with both prevalent subclinical CVD and incident clinical CVD events. Presence of subclinical CVD was determined using a comprehensive panel of diagnostic tests used to assess cardiac and vascular structure and function. Individuals with the highest (>5 p.p.m.) compared with lowest (≤4 p.p.m.) CO exposure were more likely to have subclinical CVD [odds ratios (OR): 1.67, 95% CI: 1.32-2.12; P < 0.001]. During the follow-up period (mean 5 ± 3 years), 193 individuals developed overt CVD. Individuals with both high CO levels and any baseline subclinical CVD developed overt CVD at an almost four-fold higher rate compared with those with low CO levels and no subclinical disease (22.1 vs. 6.3%). Notably, elevated CO was associated with incident CVD in the presence [hazards ration (HR): 1.83, 95% CI: 1.08-3.11; P = 0.026] but not in the absence (HR: 0.80, 95% CI: 0.42-1.53; P = 0.51) of subclinical CVD (Pinteraction = 0.019). Similarly, subclinical CVD was associated with incident CVD in the presence of high but not low CO exposure.

CONCLUSION

Our findings in a community-based sample suggest that elevated CO is a marker of greater subclinical CVD burden and, furthermore, a potential key component in the progression from subclinical to clinical CVD.