Roles for platelet-activating factor and *NO-derived oxidants causing neutrophil adherence after CO poisoning

Carbon monoxide affects early cardiac development in an avian model

INTRODUCTION

Carbon monoxide (CO) is a toxic gas that can be lethal in large doses and may also cause physiological damage in lower doses. Epidemiological studies suggest that CO in lower doses over time may impact on embryo development, in particular cardiac development, however other studies have not observed this association.

METHODS

Here, we exposed chick embryos in ovo to CO at three different concentrations (3, 9, 18 ppm) plus air control (4 protocols in total) for the first 9 days of development, at which point we assessed egg and embryo weight, ankle length, developmental stage, heart weight, ventricular wall thickness, ventricular-septal thickness and atrial wall thickness.

RESULTS

We found that heart weight was reduced for the low and moderate exposures compared to air, that atrial wall and ventricular wall thickness was increased for the moderate and high exposures compared to air and that ventricular septal thickness was increased for low, moderate and high exposures compared to air. Ventricular wall thickness was also significantly positively correlated with absolute CO exposures across all protocols.

CONCLUSIONS

This intervention study thus suggests that CO even at very low levels may have a significant impact on cardiac development.

Carbon Monoxide Poisoning: From Microbes to Therapeutics

Carbon monoxide (CO) poisoning leads to 50,000-100,000 emergency room visits and 1,500-2,000 deaths each year in the United States alone. Even with treatment, survivors often suffer from long-term cardiac and neurocognitive deficits, highlighting a clear unmet medical need for novel therapeutic strategies that reduce morbidity and mortality associated with CO poisoning. This review examines the prevalence and impact of CO poisoning and pathophysiology in humans and highlights recent advances in therapeutic strategies that accelerate CO clearance and mitigate toxicity. We focus on recent developments of high-affinity molecules that take advantage of the uniquely strong interaction between CO and heme to selectively bind and sequester CO in preclinical models. These scavengers, which employ heme-binding scaffolds ranging from organic small molecules to hemoproteins derived from humans and potentially even microorganisms, show promise as field-deployable antidotes that may rapidly accelerate CO clearance and improve outcomes for survivors of acute CO poisoning.

Chronic carbon monoxide poisoning. A report of two cases

If acute carbon monoxide poisoning is a well-known emergency situation, this is not the case for chronic poisoning. The missed diagnosis of acute CO poisoning is a well-known problem but the identification of a chronic poisoning is very challenging. Knowledge and awareness of chronic poisoning is less defined and probably there is a great number of patients with undiagnosed chronic CO poisoning. It is possible that in case of missed diagnosis because of non-specific symptoms, chronic CO poisoning could be responsible for significant morbidity. We describe the case of a married couple who were rescued almost simultaneously, to show this clinical condition.

Myocardial Injury and Fibrosis From Acute Carbon Monoxide Poisoning: A Prospective Observational Study

OBJECTIVES

This study sought to evaluate the prevalence and patterns of late gadolinium enhancement (LGE) after carbon monoxide (CO) poisoning using cardiac magnetic resonance (CMR) imaging (CMRI) and transthoracic echocardiography (TTE).

BACKGROUND

In acute CO poisoning, cardiac injury can predict mortality. However, it remains unclear why increased mortality and cardiovascular events occur despite normalization of CO-induced elevated troponin I (TnI) and cardiac dysfunction.

METHODS

Patients with acute CO poisoning with elevated TnI were evaluated. CMRI was performed within 7 days of CO exposure and after 4 to 5 months. Patients were divided into LGE (n = 72; 69.2%) and no-LGE (n = 32; 30.8%) groups.

RESULTS

In the LGE group, 39.4%, 4.8%, and 25.0% of patients exhibited midwall, subendocardial, and right ventricular insertion point injury, respectively. Diffuse injury was observed in 22.1% of patients, and 67.6% of the 37 patients who underwent follow-up CMRI showed no interval change. On TTE, baseline left ventricular ejection fraction and global longitudinal strain were significantly deteriorated in the LGE group; serial TTE within 7 days indicated that only left ventricular global longitudinal strain remained significantly deteriorated. Three cases of mortality occurred in the LGE group during the 1-year follow-up.

CONCLUSIONS

The LGE prevalence in patients with acute CO poisoning with elevated TnI levels, with no underlying cardiovascular diseases and eligible for CMRI, was 69.2%; this proportion primarily comprised patients with a midwall injury. Of the 37 patients who underwent follow-up CMRI, most chronic phase images showed no interval change. Myocardial fibrosis detected on CMR images was related to acute myocardial dysfunction and subacute deterioration of myocardial strain on TTE. (Cardiac Magnetic Resonance Image in Acute Carbon Monoxide Poisoning; NCT04419298).

Myocardial Repolarization Parameters and Neutrophil-to-Lymphocyte Ratio are Associated with Cardiotoxicity in Carbon Monoxide Poisoning

The present study aims to examine the clinical values of complete blood count (CBC) bioindicators and corrected QT (QT_c), T_peak - T_end interval (T_p-e), T_{peak dispersion} (T_{p disp}), and T_p-e/QT ratio that are the parameters of myocardial repolarization (M-rep) for cardiotoxicity, which develops due to acute carbon monoxide (CO) intoxication in patients admitted to the emergency service. This retrospective, cross-sectional, observational, and single-center study was conducted between April and June 2019. Statistical analysis was performed using the SPSS 23.0 software. Data of 234 participants were analyzed. Of these, 54.9% (n = 129) were female. Neutrophil-to-lymphocyte ratio (NLR), QT_c, T_p-e values were significantly high in the CO intoxication group (p < 0.001, p < 0.001, and p < 0.001, respectively), whereas T_p-e/QT_c ratio was significantly lower in the CO intoxication group than that in the control group (p < 0.001). NLR, T_p-e, T_{p disp} values were significantly high in the myocardial injury (M-inj) group (p < 0.001, p = 0.003, and p = 0.018, respectively). Furthermore, T_p-e/QT_c ratio was significantly low in the M-inj group (p = 0.002). M-rep parameters and NLR are associated with CO intoxication and the development of M-inj. Moreover, these bioindicators and can provide clinicians an early indication of M-inj.

Oligodendrocyte dysfunction and regeneration failure: A novel hypothesis of delayed encephalopathy after carbon monoxide poisoning

Carbon monoxide (CO) poisoning usually causes brain lesions and delayed encephalopathy, also known as delayed neurological sequelae (DNS). Demyelination of white matter (WM) is one of the most common sites of abnormalities in patients with DNS, but its mechanisms remain unclear. Oligodendrocytes (OLs) are myelinated cells that ensure the rapid conduction of neuronal axon signals and provide the nutritional factors necessary for maintaining nerve integrity in the central nervous system (CNS). OLs readily regenerate and replace damaged myelin membranes around axons in the adult mammalian CNS following demyelination. The ability to regenerate OLs depends on the availability of precursor cells (OPCs) in the CNS of adults. Multiple injury-related signals can induce OPC expansion followed by OL differentiation, axonal contact and myelin regeneration (remyelination). Therefore, OL dysfunction and regeneration failure in the deep WM of the brain are the key pathophysiological mechanisms leading to delayed brain injury after CO poisoning. CO-induced toxicity may interfere with OL function and render OPCs unable to regenerate OLs through some unclear mechanisms, leading to progressive demyelinating damage and resulting in DNS. In the future, combination therapies to reduce OL damage and promote OPC differentiation and remyelination may be important for the prevention and treatmentof DNS after CO poisoning.

Predicting of neuropsychosis in carbon monoxide poisoning according to the plasma troponin, COHb, RDW and MPV levels: Neuropsychoses in carbon monoxide poisoning

OBJECTIVE

Carbon monoxide (CO) poisoning is very common worldwide. In this study, we aimed to evaluate the predictivity of neuro psychosis in carbon monoxide poisoning by the admission levels of red cell distribution (RDW), mean platelet volume (MPV) and troponin I levels which can be measured quickly and easily in the emergency department (ED).

PATIENTS AND METHODS

This single center observational study included a total of 216 consecutive patients who presented to the ED due to CO poisoning between January 2009 and December 2013. The diagnosis of CO poisoning was made according to the medical history and carboxyhemoglobin (COHb) level of >5%. According to the carboxyhemoglobin levels, the patients were classified as mildly (COHb < 20%) and severely poisoned (COHb > 20%). In addition, patients were divided into 2 groups, i.e., those with positive (>0.05 ng/mL for our laboratory) and negative (<0.05 ng/mL for our laboratory) troponin levels.

RESULTS

Patients mean age was 52.58 ± 10.58. 57.9% of the patients had high troponin levels and 51.9% were poisoned severely according to COHb levels. Patients with positive troponin and COHb had longer CO exposure time and higher neutrophil, lymphocyte, mean platelet volume (MPV), COHb and red cell distribution width (RDW) levels at the index admission following CO poisoning than patients with negative troponin (p < 0.05). Age, COHb level, CO exposure time, MPV and RDW (p = 0.001, p < 0.05) remained associated with an increased risk of troponin positivity following adjustment for the variables that were statistically significant.

CONCLUSIONS

In patients presenting to the ED with CO poisoning, RDW and MPV can be helpful for risk stratification of neuropsychosis.

The usefulness of diffusion-weighted magnetic resonance imaging performed in the acute phase as an early predictor of delayed neuropsychiatric sequelae in acute carbon monoxide poisoning

Delayed onset of neuropsychiatric symptoms after apparent recovery from acute carbon monoxide (CO) poisoning has been described as delayed neuropsychiatric sequelae (DNS). No previous study has determined whether early use of diffusion-weighted magnetic resonance imaging (DWI) can predict which patients will develop DNS in the acute CO poisoning. This retrospective observational study was performed on adult patients with acute CO poisoning consecutively treated over a 17-month period. All included patients with acute CO poisoning underwent DWI to evaluate brain injury within 72 h after CO exposure. DWI was evaluated as follows: (1) presence of pathology, (2) number of pathologies, (3) asymmetry, and (4) location of pathology. Patients were divided into two groups. The DNS group was composed of patients with delayed sequelae, while the non-DNS group included patients with no sequelae. A total of 102 patients with acute CO poisoning were finally enrolled in this study. DNS developed in 10 patients (9.8%). Between the DNS group and the non-DNS group, presence of pathology on DWI and initial Glasgow Coma Scale (GCS) showed significant difference. There was also a statistical difference between the non-DNS group and DNS group in terms of CO exposure time, troponin I, rhabdomyolysis, acute kidney injury, and pneumonia. The presence of pathology in DWI and initial GCS (cutoff: <12) at the emergency department served as an early predictors of DNS.

G-CSF administration attenuates brain injury in rats following carbon monoxide poisoning via different mechanisms

Acute severe carbon monoxide (CO) poisoning induces hypoxia that leads to cardiovascular and nervous systems disturbances. Different complex mechanisms lead to CO neurotoxicity including lipid peroxidation, inflammatory and immune-mediated reactions, myelin degeneration and finally neuronal apoptosis and necrosis. Granulocyte colony-stimulating factor (G-CSF) is considered to be a novel neuroprotective agent. In this study, we evaluated the efficacy of G-CSF therapy on CO neurotoxicity in rats with acute CO poisoning. Rats were exposed to 3000 ppm CO in air (0.3%) for 1 h, and then different doses (50,100, and 150 µg/kg) of G-CSF or normal saline were administrated intraperitoneally. Water content of brain as an indicator for total edema and blood brain barrier integrity (Evans blue extravasation) were evaluated. Malondialydehyde was determined in order to evaluate the effect of G-CSF on CO-induced lipid peroxidation in brain tissues. Also, the effect of G-CSF on myeloperoxidase activity in the brain tissue was evaluated. The effect of G-CSF administration on induced apoptosis in the brain was measured using TUNEL method. To evaluate the level of MBP, STAT3 and pSTAT3 and HO-1 proteins and the effect of G-CSF on these proteins Western blotting was carried out. G-CSF reduced water content of the edematous poisoned brains (100 µg/kg) and BBB permeability (100 and 150 µg/kg) (P < 0.05). G-CSF (150 µg/kg) reduced the MDA level in the brain tissues (P < 0.05 as compared to CO poisoned animals). G-CSF did not decrease the MPO activity after CO poisoning in any doses. G-CSF significantly reduced the number of apoptotic neurons and Caspase 3 protein levels in the brain. Western blotting results showed that G-CSF treatment enhanced expression of HO-1 and MBP, STAT3 and pSTAT3 proteins in the brain tissues. Based on our results, a single dose of G-CSF immediately after CO poisoning significantly attenuates CO neurotoxicity via different mechanisms. © 2015 Wiley Periodicals, Inc. Environ Toxicol 32: 37-47, 2017.

Single Versus Multiple Hyperbaric Sessions for Carbon Monoxide Poisoning in a Murine Model

Hyperbaric oxygen (HBO) has been advocated for treatment of acute carbon monoxide (CO) poisoning. There exists considerable debate as to whether HBO prevents delayed neurologic sequelae (DNS) due to CO poisoning. Additionally, existing data in the literature supporting HBO efficacy do not identify an optimal number of HBO treatments. We sought to determine in a mouse model whether there is a difference between one versus multiple HBO sessions for the prevention of DNS. Fifty mice were randomized into five groups of ten mice each: (1) control, receiving no CO exposure or treatment; (2) CO poisoned, receiving no treatment (CO group); (3) CO poisoned, receiving normobaric oxygen for 58 min following the end of exposure (CO + NBO group); (4) CO poisoned, followed by one session of HBO(CO + HBO1); and (5) CO poisoned, followed by three HBO treatment sessions, one every 6 h (CO + HBO3). Prior to poisoning, all animals were trained in step-down latency (SDL) and step-up latency (SUL) tasks. One week after exposure and treatment, all five groups were retested to evaluate the retention of this training. There was no difference detected among groups in SDL (p = 0.67 among all groups) when evaluated using a Kruskal-Wallis test. There was a significant difference among groups in SUL (p = 0.027 among all groups) when evaluated using a Kruskal-Wallis test. When individual groups were compared using a Wilcoxon signed-rank test with Bonferroni correction, there were no statistically significant differences in either SDL or SUL. There was no difference between groups treated with either one or three HBO sessions. One possibility to explain this might be that HBO sessions administered some time after a CO exposure may enhance the lipid peroxidation cascade and worsen neurologic outcomes; alternatively, HBO may simply impart no benefit when compared to NBO.

Correlation of computed tomography, magnetic resonance imaging and clinical outcome in acute carbon monoxide poisoning

BACKGROUND AND OBJECTIVES

Carbon monoxide is a toxic gas for humans and is still a silent killer in both developed and developing countries. The aim of this case series was to evaluate early radiological images as a predictor of subsequent neuropsychological sequelae, following carbon monoxide poisoning.

CASE 1

After carbon monoxide exposure, early computed tomography scans and magnetic resonance imaging findings of a 52-year-old woman showed bilateral lesions in the globus pallidus. This patient was discharged and followed for 90 days. The patient recovered without any neurological sequela.

CASE 2

In a 58-year-old woman exposed to carbon monoxide, computed tomography showed lesions in bilateral globus pallidus and periventricular white matter. Early magnetic resonance imaging revealed changes similar to that like in early tomography images. The patient recovered and was discharged from hospital. On the 27th day of exposure, the patient developed disorientation and memory impairment. Late magnetic resonance imaging showed diffuse hyperintensity in the cerebral white matter.

CONCLUSION

White matter lesions which progress to demyelination and end up in neuropsychological sequelae cannot always be diagnosed by early computed tomography and magnetic resonance imaging in carbon monoxide poisoning.

The role of reactive oxygen species and oxidative stress in carbon monoxide toxicity: an in-depth analysis

The underlying mechanism of the central nervous system (CNS) injury after acute carbon monoxide (CO) poisoning is interlaced with multiple factors including apoptosis, abnormal inflammatory responses, hypoxia, and ischemia/reperfusion-like problems. One of the current hypotheses with regard to the molecular mechanism of CO poisoning is the oxidative injury induced by reactive oxygen species, free radicals, and neuronal nitric oxide. Up to now, the relevant mechanism of this injury remains poorly understood. The weakening of antioxidant systems and the increase of lipid peroxidation in the CNS have been implicated, however. Accordingly, in this review, we will highlight the relationship between oxidative stress and CO poisoning from the perspective of forensic toxicology and molecular toxicology.

Correlation of defects in regional cerebral blood flow determined by 99mTc SPECT with residual neurocognitive testing abnormalities during and 3 months post exposure in acutely poisoned patients with organophosphates

INTRODUCTION

Following acute organophosphate exposure, morphological changes in certain regions of the brain have been reported to develop within a few hours and involve neuronal degeneration. Single photon emission computed tomography (SPECT) has been used to determine changes in the regional cerebral blood flow and attempts have been made to correlate these changes with long-term neurological sequelae.

PURPOSE OF STUDY

The aim of the study was to determine changes in the regional cerebral blood flow by 99mTc-ECD SPECT following acute organophosphate poisoning and to correlate these defects with abnormalities in neurocognitive testing carried out during admission and at 3 months post exposure, in order to determine whether any changes in the cerebral blood flow could help in predicting future development of neurocognitive deficit.

PATIENTS AND METHODS

Twenty-eight patients with acute organophosphorous poisoning were included in the study. The inclusion criteria were a history of ingestion or accidental exposure, clinical features of cholinergic crises, and low serum acetylcholinesterase (AChE). Twenty age- and sex-matched patients from a previous study were used as controls for the neurocognitive tests. There were no controls for SPECT.

RESULTS

Of the 28 patients studied, 27 had abnormalities in the regional cerebral blood flow on SPECT with men having significantly higher abnormalities than women (p < 0.05). The right side of the brain had more defects than the left, with the occipital lobes being the most commonly involved. Of seven neurocognitive function tests carried out on patients who had regional cerebral blood flow defects during admission, abnormalities were observed in six tests. In 18 of 26 patients who could be tested at 3 months post exposure, improvement was observed in Trail B and Visual retention tests. However, others tests remained significantly abnormal.

CONCLUSION

We conclude that a single episode of clinically significant organophosphate intoxication can lead to persistent residual neurocognitive deficits. Detection of regional cerebral blood flow defects on 99mTc-ECD SPECT can possibly help in predicting long-term deficits in neurocognitive functions in such patients.

Dynamic changes of heme oxygenase-1 in the hippocampus of rats after acute carbon monoxide poisoning

Heme oxygenase-1 (HO-1), an inducible enzyme, degrades heme to carbon monoxide (CO), iron, and bilirubin. We have investigated the relationship among HO-1 protein expression, HO activity, and CO concentrations in the hippocampus of CO-exposed rats. Western blotting and immunohistochemistry revealed that the enzyme is predominantly localized in hippocampal CA1 and CA3 pyramidal cells and in granule cells of the dentate gyrus. HO enzyme activity was reduced immediately following CO exposure, while expression of HO-1 protein was consistently upregulated in a time-dependent manner. Local CO concentrations in hippocampus rose immediately following exposure, but the elevation was maintained for ~20 h despite the decline in blood carboxyhemoglobin levels toward baseline. We suggest that CO initially inhibits HO enzyme activity, whereas at later time points the inhibition is released and local CO generation is maintained by the activity of the endogenous HO enzyme. And the noninducible form of heme oxygenase, HO-2, was not altered following CO administration. Together these results indicate that the HO/CO pathway in the rat hippocampus is induced by acute CO exposure; local CO production may play a regulatory role in brain injury following CO poisoning.

Impaired mitochondrial respiration and protein nitration in the rat hippocampus after acute inhalation of combustion smoke

Survivors of massive inhalation of combustion smoke endure critical injuries, including lasting neurological complications. We have previously reported that acute inhalation of combustion smoke disrupts the nitric oxide homeostasis in the rat brain. In this study, we extend our findings and report that a 30-minute exposure of awake rats to ambient wood combustion smoke induces protein nitration in the rat hippocampus and that mitochondrial proteins are a sensitive nitration target in this setting. Mitochondria are central to energy metabolism and cellular signaling and are critical to proper cell function. Here, analyses of the mitochondrial proteome showed elevated protein nitration in the course of a 24-hour recovery following exposure to smoke. Mass spectrometry identification of several significantly nitrated mitochondrial proteins revealed diverse functions and involvement in central aspects of mitochondrial physiology. The nitrated proteins include the ubiquitous mitochondrial creatine kinase, F1-ATP synthase alpha subunit, dihydrolipoamide dehydrogenase (E3), succinate dehydrogenase Fp subunit, and voltage-dependent anion channel (VDAC1) protein. Furthermore, acute exposure to combustion smoke significantly compromised the respiratory capacity of hippocampal mitochondria. Importantly, elevated protein nitration and reduced mitochondrial respiration in the hippocampus persisted beyond the time required for restoration of normal oxygen and carboxyhemoglobin blood levels after the cessation of exposure to smoke. Thus, the time frame for intensification of the various smoke-induced effects differs between blood and brain tissues. Taken together, our findings suggest that nitration of essential mitochondrial proteins may contribute to the reduction in mitochondrial respiratory capacity and underlie, in part, the brain pathophysiology after acute inhalation of combustion smoke.

Intravascular neutrophil activation due to carbon monoxide poisoning

RATIONALE

We hypothesized that platelet-neutrophil interactions occur as a result of acute carbon monoxide (CO) poisoning, and subsequent neutrophil activation triggers events that cause neurologic sequelae.

OBJECTIVES

To identify platelet-neutrophil interactions and neutrophil activation in patients and in animal models, and to establish the association between these intravascular events and changes linked to CO-mediated neurologic sequelae in an animal model.

MEASUREMENTS AND MAIN RESULTS

Blood was obtained from 50 consecutive patients. Abnormalities were variable depending on the carboxyhemoglobin level at study admission and duration of CO exposure. Platelet-neutrophil aggregates were detected and plasma myeloperoxidase (MPO) concentration was significantly elevated in those with confirmed CO poisoning. Among patients exposed to CO for over 3 h, flow cytometry scans of neutrophils revealed increased surface expression of CD18 and, in some groups, MPO on the cell surface. Animal models revealed consistent evidence of platelet-neutrophil aggregates, neutrophil activation and surface MPO, and plasma MPO elevation. MPO was deposited along the brain vascular lining and colocalized with nitrotyrosine. CO poisoning caused abnormalities in the charge pattern of myelin basic protein (MBP), changes linked to adaptive immunologic responses responsible for neurologic sequelae in this model. Changes did not occur in thrombocytopenic rats, those receiving tirofiban to inhibit platelet-neutrophil interactions, or those receiving L-nitroarginine methyl ester to inhibit nitric oxide synthesis. Alterations in MBP did not occur in CO-poisoned knockout mice lacking MPO.

CONCLUSIONS

Acute CO poisoning causes intravascular neutrophil activation due to interactions with platelets. MPO liberated by neutrophils mediates perivascular oxidative stress, which is linked to immune-mediated neurologic sequelae.

Toxicity Associated with Carbon Monoxide

Carbon monoxide is an insidious poison that accounts for thousands of deaths each year in North America. Clinical effects maybe diverse and include headache, dizziness, nausea, vomiting,syn-cope, seizures, coma, dysrhythmias, and cardiac ischemia. Children, pregnant women, and patients who have underlying cardiovascular disease are particularly at risk for adverse out-comes. Treatment consists of oxygen therapy, supportive care, and, in selected cases, hyperbaric oxygen therapy.

Carbon monoxide poisoning

CO is an ubiquitous poison with many sources of exposure. CO poisoning produces diverse signs and symptoms that are often subtle and may be easily misdiagnosed. Failure to diagnose CO poisoning may result insignificant morbidity and mortality and permit continued exposure to a dangerous environment. Treatment of CO poisoning begins with inhalation of supplemental oxygen and aggressive supportive care. HBOT accelerates dissociation of CO from hemoglobin and may also prevent DNS. Absolute indications forHBOT for CO poisoning remain controversial, although most authors would agree that HBOT is indicated in patients who are comatose or neurologically abnormal, have a history of LOC with their exposure, or have cardiac dysfunction. Pregnancy with an elevated CO-Hgb level(>15%-20%) is also widely, considered an indication for treatment.HBOT may be considered in patients who have persistent symptoms despite NBO, metabolic acidosis, abnormalities on neuropsychometric testing, or significantly elevated levels. The ideal regimen of oxygen therapy has yet to be determined, and significant controversy exists regarding HBOTtreatment protocols. Often the local medical toxicologist, poison control center, or hyperbaric unit may assist the treating physician with decisions regarding therapy.

Effects of Carbon Monoxide Poisoning on Neutrophil Responses in Patients Treated with Hyperbaric Oxygen

Background

Carbon monoxide (CO) poisoning can cause tissue injury. Neutrophil granulocytes have been proposed to contribute to the injury, which may be ameliorated by hyperbaric oxygen (HBO2) treatment. We sought to assess the relationship between acute CO poisoning and blood neutrophil count, plasma cytokine, and Cortisol responses, as well as the mechanism behind the observed beneficiary effects of HBO2 treatment.

Methods

Eight patients (age 26–82 years) with severe acute CO poisoning were enrolled, concomitant with eight healthy controls (age 27–42 years), in a prospective, controlled, clinical study. The patients were given three HBO2 treatments (2.8 atmospheres absolute, 100 minutes) within the first 24 hours. The controls were given identical simultaneous HBO2 treatments. Venous blood samples were taken before and after each treatment.

Results

At the start of the HBO2 treatment, patients displayed significantly higher blood neutrophil counts ( p < .0001) and plasma Cortisol levels (p = .020) than controls, but the two groups had similar values for interleukin-8, granulocyte colony-stimulating factor (G-CSF), neutrophil H2O2 generation, and CD16 and CD18 surface expression. During the observation time, neutrophil H2O2 accumulation declined in patients and in controls ( p = .031), whereas the up-regulation of CD18 expression increased ( p = .002) in both groups. Moreover, G-CSF levels became significantly higher in patients than in controls ( p = .015). G-CSF levels also correlated significantly with neutrophil counts.

Conclusion

CO poisoning was associated with discrete changes of blood neutrophil counts, Cortisol, and G-CSF plasma concentrations. HBO2 treatment modulated neutrophil generation of H2O2 and surface expression of CD18. These changes may be part of the cascade of events leading to the sequelae of CO poisoning and their attenuation by HBO2.

Carbon monoxide poisoning

CO is an insidious poison with many sources of exposure. CO poisoning produces diverse signs and symptoms, which often are subtle and can be misdiagnosed easily. Failure to diagnose CO poisoning may result insignificant morbidity and mortality and allow continued exposure to a dangerous environment. In the ED, a high index of suspicion must be maintained for occult CO exposure. Headache, particularly when associated with certain environments, and flulike illness in the wintertime with symptomatic cohabitants should raise the index of suspicion in the ED significantly for occult CO poisoning. Emergency treatment of CO poisoning begins with inhalation of supplemental oxygen and aggressive supportive care. HBOT accelerates dissociation of CO from hemoglobin and may prevent DNS. Absolute indications for HBOT for CO poisoning remain controversial, although most would agree that HBOT is indicated in patients who are comatose, are neurologically abnormal, have a history of loss of consciousness with their exposure, or have cardiac dysfunction. Pregnancy with an elevated CO-Hgb level (>15-20%) also is widely considered an indication for treatment. HBOT may be considered in patients who have persistent symptoms despite NBO, metabolic acidosis, abnormalities on neuropsychometric testing, or significantly elevated levels. The ideal regimen of oxygen therapy has yet to be determined, and significant controversy exists regarding HBOT protocols. The emergency physician may be confronted with the difficult decision regarding disposition and even transfer to a hyperbaric facility. Often the local medical toxicologist, poison control center, or hyperbaric unit can assist the emergency physician with the decision-making process.

Delayed neuropathology after carbon monoxide poisoning is immune-mediated

The neuropathological sequelae of carbon monoxide (CO) poisoning cannot be explained by hypoxic stress alone. CO poisoning also causes adduct formation between myelin basic protein (MBP) and malonylaldehyde, a reactive product of lipid peroxidation, resulting in an immunological cascade. MBP loses its normal cationic characteristics, and antibody recognition of MBP is altered. Immunohistochemical evidence of degraded MBP occurs in brain over days, along with influx of macrophages and CD-4 lymphocytes. Lymphocytes from CO-poisoned rats subsequently exhibit an auto-reactive proliferative response to MBP, and there is a significant increase in the number of activated microglia in brain. Rats rendered immunologically tolerant to MBP before CO poisoning exhibit acute biochemical changes in MBP but no lymphocyte proliferative response or brain microglial activation. CO poisoning causes a decrement in learning that is not observed in immunologically tolerant rats. These results demonstrate that delayed CO-mediated neuropathology is linked to an adaptive immunological response to chemically modified MBP.

Ability of eugenol to reduce tongue edema induced by Dieffenbachia picta Schott in mice

Dieffenbachia picta Schott (Araceae), known in Brazil as "comigo-ninguém-pode" is an ornamental plant with toxic properties. Its juice, when chewed, causes a painful edema of the oral mucous membranes, buccal ulcerations and tongue hypertrophy. This acute inflammation sometimes becomes severe enough to produce glottis obstruction, respiratory compromise and death. Eugenol (4-alil-2-metoxiphenol), the essential oil extracted from Caryophyllus aromaticus (Myrtaceae) is widely used in odontology. In this study, our objective was to standardize, in mice, a measurable methodology for the tongue edema induced by the topical application of the D. picta stem juice; evaluate the effects of eugenol in this model and compare the results with emergency treatment used in hospitals. Our results show that in spite of a small increase in edema a few minutes after administration, emergency treatment reduced by 70% the overall edema. When compared with the combination of the above drugs, eugenol, even at the smallest dose of 5 microg/kg, regardless of the chosen administration route, or the moment the treatment began, presents better results in the reduction and inhibition of the tongue edema induced by the D. picta juice.

Role of melatonin in carbon monoxide-induced hypoxemia

Melatonin (MEL) works in tandem with serotonin (5HT), where an equilibrium exists in perfect health. Under stress or in crisis, it may be that the production of MEL predominates in conjunction with ever increasing production of reactive oxygen species (ROS), may lead to hypoxemia and consequently, to metabolic disruption. The Melatonin Hypothesis could offer an explanation towards certain clinical observation and may support the Catacholamine Hypothesis in the development of depression but it is the role played by carbon monoxide (CO) in inducing hypoxemia which may result in the Cascade Effect that could in turn explain the development of neurodegenerative, neurodevelopmental as well as immune dysfunctional type disorders, prevalent today. CO-induced hypoxemia is an important aspect in any discussion of cell integrity as CO is formed endogenously from the degradation of erythrocytic heme, any hemolytic disturbance or lipid peroxidation, may increase the level in blood. CO, in inducing hypoxemia, causes the generation of large quantities of hydroxyl (-OH) which could damage specific amino acid and disorder protein metabolism that may result in the creation of toxic metabolites. Hydroxyl damage is emerging as the precursor to low-grade inflammation in the presence of C Reactive Protein (CRP) that is currently speculated in the etiology of many known disorders. As disordered protein metabolism may play a crucial role in the formation of the cascade, the hypothesis aims to address the issues of cell viability and the process of cell replication in the event where cell integrity is severely compromised in the face of apoptotic and/or necrotic damage, as the intra-cellular and extra-cellular environments are becoming increasingly hostile. Where -OH damage to specific amino acid in protein may contribute to the Cascade Effect, the hypothesis goes further to explain the importance of the Circardian Cycle and the role of paradoxical sleep, by taking into consideration the need for repair and for regeneration in order to maintain morphology as any cellular event that depends on a redox state is likely to be compromised in an event of hypoxemia. As MEL enters a cell readily because of its high lipid solubility, the role of MEL becomes clear as in its diversity, MEL is a potent oxygen radical scavenger that operates throughout the cell.

Neuronal nitric oxide synthase and N-methyl-D-aspartate neurons in experimental carbon monoxide poisoning

We measured changes in nitric oxide (NO) concentration in the cerebral cortex during experimental carbon monoxide (CO) poisoning and assessed the role for N-methyl-d-aspartate receptors (NMDARs), a glutamate receptor subtype, with progression of CO-mediated oxidative stress. Using microelectrodes, NO concentration was found to nearly double to 280 nM due to CO exposure, and elevations in cerebral blood flow, monitored as laser Doppler flow (LDF), were found to loosely correlate with NO concentration. Neuronal nitric oxide synthase (nNOS) activity was the cause of the NO elevation based on the effects of specific NOS inhibitors and observations in nNOS knockout mice. Activation of nNOS was inhibited by the NMDARs inhibitor, MK 801, and by the calcium channel blocker, nimodipine, thus demonstrating a link to excitatory amino acids. Cortical cyclic GMP concentration was increased due to CO poisoning and shown to be related to NO, versus CO, mediated guanylate cyclase activation. Elevations of NO were inhibited when rats were infused with superoxide dismutase and in rats depleted of platelets or neutrophils. When injected with MK 801 or 7-nitroindazole, a selective nNOS inhibitor, rats did not exhibit CO-mediated nitrotyrosine formation, myeloperoxidase (MPO) elevation (indicative of neutrophil sequestration), or impaired learning. Similarly, whereas CO-poisoned wild-type mice exhibited elevations in nitrotyrosine and myeloperoxidase, these changes did not occur in nNOS knockout mice. We conclude that CO exposure initiates perivascular processes including oxidative stress that triggers activation of NMDA neuronal nNOS, and these events are necessary for the progression of CO-mediated neuropathology.

NO produced by endothelial NO synthase is a mediator of delayed preconditioning-induced endothelial protection

Preconditioning with brief periods of ischemia-reperfusion (I/R) induces a delayed protection of coronary endothelial cells against reperfusion injury. We assessed the possible role of nitric oxide (NO) produced during prolonged I/R as a mediator of this endothelial protection. Anesthetized rats were subjected to 20-min cardiac ischemia/60-min reperfusion, 24 h after sham surgery or cardiac preconditioning (1 x 2-min ischemia/5-min reperfusion and 2 x 5-min ischemia/5-min reperfusion). The nonselective NO synthase (NOS) inhibitor l-NAME, the selective inhibitors of neuronal (7-nitroindazole) or inducible (1400W) NOS, or the peroxynitrite scavenger seleno-l-methionine were administered 10 min before prolonged ischemia. Preconditioning prevented the reperfusion-induced impairment of coronary endothelium-dependent relaxations to acetylcholine (maximal relaxation: sham 77 +/- 3; I/R 44 +/- 6; PC 74 +/- 5%). This protective effect was abolished by l-NAME (41 +/- 7%), whereas 7-NI, 1400W or seleno-l-methionine had no effect. The abolition of preconditioning by l-NAME, but not by selective nNOS or iNOS inhibition, suggests that NO produced by eNOS is a mediator of delayed endothelial preconditioning.

Endothelial transcytosis of myeloperoxidase confers specificity to vascular ECM proteins as targets of tyrosine nitration

Nitrotyrosine formation is a hallmark of vascular inflammation, with polymorphonuclear neutrophil-derived (PMN-derived) and monocyte-derived myeloperoxidase (MPO) being shown to catalyze this posttranslational protein modification via oxidation of nitrite (NO(2)(-)) to nitrogen dioxide (NO(2)(*)). Herein, we show that MPO concentrates in the subendothelial matrix of vascular tissues by a transcytotic mechanism and serves as a catalyst of ECM protein tyrosine nitration. Purified MPO and MPO released by intraluminal degranulation of activated human PMNs avidly bound to aortic endothelial cell glycosaminoglycans in both cell monolayer and isolated vessel models. Cell-bound MPO rapidly transcytosed intact endothelium and colocalized abluminally with the ECM protein fibronectin. In the presence of the substrates hydrogen peroxide (H(2)O(2)) and NO(2)(-), cell and vessel wall-associated MPO catalyzed nitration of ECM protein tyrosine residues, with fibronectin identified as a major target protein. Both heparin and the low-molecular weight heparin enoxaparin significantly inhibited MPO binding and protein nitrotyrosine (NO(2)Tyr) formation in both cultured endothelial cells and rat aortic tissues. MPO(-/-) mice treated with intraperitoneal zymosan had lower hepatic NO(2)Tyr/tyrosine ratios than did zymosan-treated wild-type mice. These data indicate that MPO significantly contributes to NO(2)Tyr formation in vivo. Moreover, transcytosis of MPO, occurring independently of leukocyte emigration, confers specificity to nitration of vascular matrix proteins.