Apoptotic and necrotic brain lesions in a fatal case of carbon monoxide poisoning

Evaluation of cadmium and mercury on cardiovascular and neurological systems: Effects on humans and fish

Chemicals are at the top of public health concerns and metals have received much attention in terms of toxicological studies. Cadmium (Cd) and mercury (Hg) are among the most toxic heavy metals and are widely distributed in the environment. They are considered important factors involved in several organ disturbances. Heart and brain tissues are not among the first exposure sites to Cd and Hg but they are directly affected and may manifest intoxication reactions leading to death. Many cases of human intoxication with Cd and Hg showed that these metals have potential cardiotoxic and neurotoxic effects. Human exposure to heavy metals is through fish consumption which is considered as an excellent source of human nutrients. In the current review, we will summarize the most known cases of human intoxication with Cd and Hg, highlight their toxic effects on fish, and investigate the common signal pathways of both Cd and Hg to affect heart and brain tissues. Also, we will present the most common biomarkers used in the assessment of cardiotoxicity and neurotoxicity using Zebrafish model.

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.

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.

Effects of Hg sublethal exposure in the brain of peacock blennies Salaria pavo: Molecular, physiological and histopathological analysis

Marine environments are affected by large amounts of toxicants among those mercury (Hg). The aim of this study was to assess potential neurotoxic effects of Hg in the peacock blenny Salaria pavo. A sublethal contamination to 66 μg HgCl₂ L^-1 over periods of 1, 4, 10 and 15 days was performed. Total Hg concentrations measured in the brain highlighted the detection of Hg at days 1 and 4 following the exposure but no concentration of the metal was further detected. Partial-length cDNA of genes coding ABC transporters (abcb1, abcc1, abcc2, abcg2) and acetylcholinesterase (ache) were characterized. Results from mRNA expression levels displayed an up-regulation of abcb1 mRNA while a down-regulation of abcc1 and abcc2 mRNA was observed. No change in abcg2 and ache mRNA expression was noted throughout the experiment. At each sampling time, Hg exposure did not affect the activity of the AChE enzyme. The histological analysis indicated that fish exhibited several damages in the optic tectum and the cerebellum and 3 reaction patterns were identified for each organ: circulatory disturbances, regressive and progressive changes. Molecular, physiological and histological biomarkers assessed in the present study highlighted that peacock blennies were able to detoxify Hg from the brain tissue by developing defense mechanisms. More globally, neurotoxic effects of a sublethal Hg exposure in the brain of peacock blennies and the adaptation capacity of this species were evaluated.

Comparative Response of Brain to Chronic Hypoxia and Hyperoxia

Two antithetic terms, hypoxia and hyperoxia, i.e., insufficient and excess oxygen availability with respect to needs, are thought to trigger opposite responses in cells and tissues. This review aims at summarizing the molecular and cellular mechanisms underlying hypoxia and hyperoxia in brain and cerebral tissue, a context that may prove to be useful for characterizing not only several clinically relevant aspects, but also aspects related to the evolution of oxygen transport and use by the tissues. While the response to acute hypoxia/hyperoxia presumably recruits only a minor portion of the potentially involved cell machinery, focusing into chronic conditions, instead, enables to take into consideration a wider range of potential responses to oxygen-linked stress, spanning from metabolic to genic. We will examine how various brain subsystems, including energetic metabolism, oxygen sensing, recruitment of pro-survival pathways as protein kinase B (Akt), mitogen-activated protein kinases (MAPK), neurotrophins (BDNF), erythropoietin (Epo) and its receptors (EpoR), neuroglobin (Ngb), nitric oxide (NO), carbon monoxide (CO), deal with chronic hypoxia and hyperoxia to end-up with the final outcomes, oxidative stress and brain damage. A more complex than expected pattern results, which emphasizes the delicate balance between the severity of the stress imposed by hypoxia and hyperoxia and the recruitment of molecular and cellular defense patterns. While for certain functions the expectation that hypoxia and hyperoxia should cause opposite responses is actually met, for others it is not, and both emerge as dangerous treatments.

Hyperbaric oxygen preserves neurotrophic activity of carbon monoxide-exposed astrocytes

In astrocytes, carbon monoxide (CO) poisoning causes oxidative stress and mitochondrial dysfunction accompanied by caspase and calpain activation. Impairment in astrocyte function can be time-dependently reduced by hyperbaric (3bar) oxygen (HBO). Due to the central role of astrocytes in maintaining neuronal function by offering neurotrophic support we investigated the hypothesis that HBO therapy may exert beneficial effect on acute CO poisoning-induced impairment in intrinsic neurotrophic activity. Exposure to 3000ppm CO in air followed by 24-72h of normoxia caused a progressive decline of gene expression, synthesis and secretion of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) to different extent. 1h treatment with 100% oxygen disclosed a pressure- and time-dependent efficacy in preserving astrocytic neurotrophic support. The beneficial effect was most evident when the astrocytes were exposed to HBO 1-5h after exposure to CO. The results further support an active role of hyperbaric, not normobaric, oxygenation in reducing dysfunction of astrocytes after acute CO poisoning. By preserving endogenous neurotrophic activity HBO therapy might promote neuronal protection and thus prevent the occurrence of late neuropsychological sequelae.

The effectiveness of oxygen therapy in carbon monoxide poisoning is pressure- and time-dependent: a study on cultured astrocytes

Carbon monoxide (CO) poisoning causes neuronal and glial apoptosis that can result in delayed neurological symptoms. The damage of brain cells can be prevented by oxygen therapy. Based on the central role of astrocytes in maintaining neuronal function and viability we investigated the toxic effects of 3000ppm CO in air followed by 24h of normoxia and evaluated the possible protective influence of 100% normobaric oxygen or 100% oxygen at a pressure of 3bar (hyperbaric) against CO poisoning in these cells. CO/normoxia caused a progressive decline of viability, increase in reactive oxygen species and decline of mitochondrial membrane potential and intracellular ATP levels in cultured rat astrocytes. Increased caspase-9, caspase-8 and calpain activity converged in activation of caspase-3/7. 1h treatment with oxygen disclosed pressure- and time-dependent efficacy in restoring astrocytic mitochondrial function and the prevention of apoptosis. The protective effect was most evident when the astrocytes were exposed to hyperbaric oxygen, but not normobaric oxygen, 1-5h after exposure to CO.

Acute mitochondrial encephalopathy reflects neuronal energy failure irrespective of which genome the genetic defect affects

Mitochondrial dysfunction and disease may arise as a result of mutations in either the mitochondrial genome itself or nuclear encoded genes involved in mitochondrial homeostasis and function. Irrespective of which genome is affected, mitochondrial encephalopathies share clinical and biochemical features suggesting common pathophysiological pathways. Two common paradigms of mitochondrial encephalopathy are mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes caused by maternally transmitted mutations of mitochondrial DNA and mitochondrial spinocerebellar ataxia and epilepsy caused by recessively inherited mutations of the nuclear-encoded DNA polymerase gamma, which replicates and repairs the mitochondrial genome. We studied and compared the disease mechanisms involved in these two syndromes. Despite having different genetic origins, their pathophysiological pathways converge on one critical event, damage to the respiratory chain leading to insufficient energy to maintain cellular homeostasis. In the central nervous system, this appears to cause selective neuronal damage leading to the development of lesions that mimic ischaemic damage, but which lack evidence of decreased tissue perfusion. Although these stroke-like lesions may expand or regress dynamically, the critical factor that dictates prognosis is the presence of epilepsy. Epileptic seizures increase the energy requirements of the metabolically already compromised neurons establishing a vicious cycle resulting in worsening energy failure and neuronal death. We believe that it is this cycle of events that determines outcome and which provides us with a mechanistic structure to understand the pathophysiology of acute mitochondrial encephalopathies and plan future treatments.

Toxic agents causing cerebellar ataxias

The cerebellum is particularly vulnerable to intoxication and poisoning, especially so the cerebellar cortex and Purkinje neurons. In humans, the most common cause of a toxic lesion to the cerebellar circuitry is alcohol related, but the cerebellum is also a main target of drug exposure (such as anticonvulsants, antineoplastics, lithium salts, calcineurin inhibitors), drug abuse and addiction (such as cocaine, heroin, phencyclidine), and environmental toxins (such as mercury, lead, manganese, toluene/benzene derivatives). Although data for the prevalence and incidence of cerebellar lesions related to intoxication and poisoning are still unknown in many cases, clinicians should keep in mind the list of agents that may cause cerebellar deficits, since toxin-induced cerebellar ataxias are not rare in daily practice. Moreover, the patient's status may require immediate therapies when the intoxication is life-threatening.

Localized cerebral energy failure in DNA polymerase gamma-associated encephalopathy syndromes

Mutations in the catalytic subunit of the mitochondrial DNA-polymerase gamma cause a wide spectrum of clinical disease ranging from infantile hepato-encephalopathy to juvenile/adult-onset spinocerebellar ataxia and late onset progressive external ophthalmoplegia. Several of these syndromes are associated with an encephalopathy that characteristically shows episodes of rapid neurological deterioration and the development of acute cerebral lesions. The purpose of this study was to investigate the nature, distribution and natural evolution of central nervous system lesions in polymerase gamma associated encephalopathy focusing particularly on lesions identified by magnetic resonance imaging. We compared radiological, electrophysiological and pathological findings where available to study potential mechanisms underlying the episodes of exacerbation and acute cerebral lesions. We studied a total of 112 magnetic resonance tomographies and 11 computed tomographies in 32 patients with polymerase gamma-encephalopathy, including multiple serial examinations performed during both the chronic and acute phases of the disease and, in several cases, magnetic resonance spectroscopy and serial diffusion weighted studies. Data from imaging, electroencephalography and post-mortem examination were compared in order to study the underlying disease process. Our findings show that magnetic resonance imaging in polymerase gamma-related encephalopathies has high sensitivity and can identify patterns that are specific for individual syndromes. One form of chronic polymerase gamma-encephalopathy, that is associated with the c.1399G > A and c.2243G > C mutations, is characterized by progressive cerebral and cerebellar atrophy and focal lesions of the thalamus, deep cerebellar structures and medulla oblongata. Acute encephalopathies, both infantile and later onset, show similar pictures with cortical stroke-like lesions occurring during episodes of exacerbation. These lesions can occur both with and without electroencephalographic evidence of concurrent epileptic activity, and have diffusion, spectroscopic and histological profiles strongly suggestive of neuronal energy failure. We suggest therefore that both infantile and later onset polymerase gamma related encephalopathies are part of a continuum.

Gases in the mitochondria

Gasomodulators - nitric oxide, carbon monoxide and hydrogen sulphide - are important physiological mediators that have been implicated in disorders such as neurodegeneration and sepsis. Some of their biological functions involve the mitochondria. In particular, their inhibition of cytochrome c oxidase has received much attention as this can cause energy depletion and cytotoxicity. However, reports that cellular energy production and cell survival are maintained even in the presence of gasomodulators are not uncommon. In both cases, modulation of mitochondrial targets by the gasomodulators appears to be an important event. We provide an overview of the effects of the gasomodulators on the mitochondria.

Low doses of carbon monoxide protect against experimental focal brain ischemia

Carbon monoxide (CO) is associated with central nervous system toxicity. However, evidence also indicates that CO can be protective, depending on its concentration. To determine if CO can be neuroprotective after ischemic brain injury, we subjected mice to transient middle cerebral artery occlusion and exposed them to different concentrations of CO. We found that in mice, low CO levels protected the brain from injury following 90-min transient focal ischemia and 48 h of reperfusion. When inhalation of 125 or 250 ppm CO began immediately at the onset of reperfusion, total hemispheric infarct volume was reduced by 32.1 +/- 8.9% and 62.2 +/- 14.4%, respectively; with an extended therapeutic window of 1-3 h after ischemia, CO inhalation also attenuated infarct volume significantly. Furthermore, early CO exposure limited brain edema formation by 3.2 +/- 0.8% (125 ppm) and 2.6 +/- 0.3% (250 ppm). Finally, CO inhalation significantly improved neurological deficit scores at 48 h of survival time after ischemia. Transient elevation of carboxyhemoglobin levels returned rapidly to baseline when CO exposure was stopped. These findings suggest a potential application of CO to treat brain ischemic stroke.

Pursuing enigmas on ischemic heart disease and sudden cardiac death

This article reviews what our colleagues have found as to how ischemic injury or cell death develop in myocardium through Ca(2+)-dependent protease calpain and how compensatory responses evolve through activation of intracellular signaling molecules including PKC isoforms, MAP kinase family enzymes and PI3 kinase. We also addressed how restraint or other psychological stress evokes hypertension and cardiovascular responses in signaling molecules or genes. Unexpectedly, carbon monoxide protects heart and cardiogenic cells against ischemia-resperfusion injury. When I think back, the unresolved cases of autopsies provided ideas for experimental study, which then taught us how the other cases died.

Basal ganglia lesions following carbon monoxide poisoning

PRIMARY OBJECTIVES

Carbon monoxide (CO) is the most common cause of poisoning and may result in basal ganglia lesions. This study reviewed the literature of carbon monoxide poisoning and basal ganglia lesions and prospectively assessed the prevalence of basal ganglia lesions in a cohort of patients with CO poisoning.

RESEARCH DESIGN

Literature review and prospective cohort study.

METHODS

This study conducted a comprehensive review of the literature and assessed 73 CO-poisoned patients for basal ganglia lesions on sequential MR scans. Magnetic resonance scans were obtained on day 1, 2 weeks and 6 months post-CO poisoning.

RESULTS

The literature review found basal ganglia lesions occur in 4-88% of subjects. Only one patient was found with globus pallidus lesions at 2 weeks and 6 months following CO poisoning, that were not present on the initial day 1 MR scan.

CONCLUSIONS

Basal ganglia lesions, including lesions of the globus pallidus, may be less common than previously reported.

Immediate oxygen therapy prevents brain cell injury in carbon monoxide poisoned rats without loss of consciousness

In CO-poisoned patients without loss of consciousness no significant long-term functional differences in outcome have been shown in any hyperbaric versus normobaric oxygen studies. Since brain histology changes cannot be studied in CO-poisoned patients we evaluated the efficacy of normobaric and hyperbaric oxygen therapy in preventing brain cell injury in CO-poisoned animals without loss of consciousness. Wistar rats without loss of consciousness after exposure to 3000ppm of CO for 60min were exposed to ambient air (group 1), 100% oxygen at a pressure of 1bar (group 2) and 100% oxygen at a pressure of 3bar (group 3). The rats were sacrificed after two weeks, brain samples were stained with hematoxylin-eosin and a percentage of pyknotic cells in hippocampus was reported. Analyses of differences in percentage of pyknotic cells between different kinds of therapy showed that the percentage of pyknotic cells of the second group (2.3+/-1.2%) treated with normobaric oxygen and the third group (4.5+/-4.0%) treated with hyperbaric oxygen were similar, and both of them were significantly different, with a much lower percentage of pyknotic cells, from the first group left on ambient air (47.7+/-10.0%). In conclusion, immediate normobaric and hyperbaric oxygen therapy equally prevents hippocampal cell injury in CO-poisoned rats without loss of consciousness.

Hypoxia-independent apoptosis in neural cells exposed to carbon monoxide in vitro

The neurotoxic effects of carbon monoxide (CO) are well known. Brain hypoxia due to the binding of CO to hemoglobin is a recognized cause of CO neurotoxicity, while the direct effect of CO on intracellular targets remains poorly understood. In the present study, we have investigated the pathways leading to neural cell death induced by in vitro exposure to CO using a gas exposure chamber that we have developed. Mouse hippocampal neurons (HT22) and human glial cells (D384) were exposed to concentrations of CO ranging from 300 to 1000 ppm in the presence of 20% oxygen. Cytotoxicity was observed after 48 h exposure to 1000 ppm, corresponding to approximately 1 microM CO in the cultured medium, as measured by gas chromatography. CO induced cell death with characteristic features of apoptosis. Exposed cells exhibited loss of mitochondrial membrane potential, release of cytochrome c into the cytosol, nuclei with chromatin condensation, and exposure of phosphatidyl serine on the external leaflet of the plasma membrane. CO also triggered activation of caspase and calpain proteases. Pre-incubation with either the pancaspase inhibitor Z-VAD-fmk (20 microM) or the calpain inhibitor E64d (25 microM) reduced by 50% the occurrence of apoptosis. When pre-incubating the cells with the two inhibitors together there was an additional reduction in the number of cells with apoptotic nuclei. These data suggest that CO causes apoptosis via activation of parallel proteolytic pathways involving both caspases and calpains. Furthermore, pre-treatment with the antioxidant MnTBAP (100 microM) significantly reduced the number of apoptotic nuclei, pointing to a critical role of oxidative stress in CO toxicity.

Effects of hypoxia on the brain: neuroimaging and neuropsychological findings following carbon monoxide poisoning and obstructive sleep apnea

Hypoxia damages multiple organ systems especially those with high oxygen utilization such as the central nervous system. The purpose of this study was to compare the neuropathological and neuropsychological effects of hypoxia in patients with either carbon monoxide poisoning or obstructive sleep apnea. Neuroimaging revealed evidence of hippocampal atrophy in both groups although a linear relationship between hippocampal volume and memory performance was found only for selected tests and only in the sleep apnea group. There were significant correlations between hippocampal volume and performance on measures related to nonverbal/information processing. Generalized brain atrophy, as measured by the ventricle-to-brain ratio, was more common in the carbon monoxide poisoning group compared to the obstructive sleep apnea group. Performance on tests of executive function improved following treatment with nasal continuous positive airway pressure treatment in the obstructive sleep apnea group but there was no associated improvement in general intellectual function. We found that hypoxia due to obstructive sleep apnea and CO poisoning resulted in neuropathological changes and neuropsychological impairments. The observed group differences provide insight into the relationship between etiology of injury, neuropathological changes, and clinical presentation.

Hypothermia attenuates delayed cortical cell death and ROS generation following CO inhalation

Carbon monoxide (CO) is the most popular cause of poisoning. The bilateral basal ganglia lesion characterizes the delayed neuronal cell death (DCD). We demonstrated there were both apoptosis and necrosis in the cortex, basal ganglia and hippocampus in a case of human CO accident. To elucidate the mechanism of DCD after CO inhalation, histological studies on the rat brain were conducted. Rats were ventilated with nitrous oxide (sham group), 10% O(2) (hypoxia group) or 1005 ppm CO (CO group) for 90 min, while the pericranial temperature was controlled at either 32, 37, or 39 degrees C during CO inhalation. After reoxygenation for 30 min, the rats were allowed to recover for 48 h. The ratio of eosinophilic and HNE-positive neurons in the cortex were higher in the CO group than in the hypoxia group at 37 degrees C, while the PaO(2) was much lower in the hypoxia than in the CO group. The damage was alleviated in the hypothermia (32 degrees C) as compared with normothermia, while the hyperthermia (39 degrees C) did not significantly increased it. CO inhalation injures neuron by reactive oxygen species (ROS), independent of hypoxia, as can be concluded from the histological comparison of DCD with HNE immunoreactivity.

Lipid peroxidation in the rat brain after CO inhalation is temperature dependent

We reported previously that 7-hydroperoxycholesterols, 7 alpha- and 7 beta-hydroperoxycholest-5-en-3 beta-ol (7 alpha-OOH and 7 beta-OOH), indicated lipid peroxidation. In the present study, we measured not only 7-hydroperoxycholesterols but also oxysterols (7 alpha- and 7 beta-hydroxycholesterol, 7 alpha-OH, and 7 beta-OH) and 3 beta-hydroxycholest-5-en-7-one (7-keto) in the brains of rats that underwent either a sham operation (control), hypoxia, or CO inhalation (1005 ppm) at 37 degrees C for 90 min followed by 48 h of recovery. The levels of 7-hydroperoxycholesterols, 7 beta-OH, and 7-keto were low in the hypoxia group, while the levels were unaltered in the CO group compared with the controls. Among the three groups of CO inhalation, these levels were high in the hyperthermia group (39 degrees C), and the 7-hydroperoxycholesterols were low in the hypothermia group (32 degrees C), compared with the control group. The blood O(2) saturation was almost normal in the hypothermia group, while it was similarly low in the hyperthermia and normothermia groups. The temperature-dependent lipid peroxidation in the brain after CO inhalation and recovery can not be explained by hypoxia due to CO-hemoglobin formation, but may contribute to the delayed neuronal death following CO inhalation. Hypothermia may be applicable to treat patients after CO inhalation.