A rat model of smoke inhalation injury: Influence of combustion smoke on gene expression in the brain

Use of extracorporeal membrane oxygenation in children with burn injury: Case report and literature review

RATIONALE

Burns are one of the most debilitating injuries in the world and one of the major causes of accidental disability and death among children. Severe burns can result in irreversible brain damage, placing patients at high risk of brain failure and high mortality. Therefore, timely diagnosis and treatment of burn encephalopathy are crucial for improving prognosis. In recent years, extracorporeal membrane oxygenation (ECMO) has been increasingly used to improve the prognosis of patients with burns. Here, we report a case of ECMO treatment in a child with burns and review the relevant literature.

PATIENT CONCERNS

A 7-year-old boy with a modified Baux score of 24 presented with asphyxia, loss of consciousness, refractory hypoxemia, and malignant arrhythmia after smoke inhalation for 1 day. Fiberoptic bronchoscopy revealed a large amount of black carbon-like substances aspirated from the trachea.

DIAGNOSES

Considering that the boy inhaled a large amount of smoke, the clinical manifestation was unclear consciousness, laboratory examination revealed continuous low blood oxygen saturation, and bronchoscopy revealed a large amount of black carbon-like substances in the trachea, thereby leading to the diagnosis of asphyxia, inhalation pneumonia, burn encephalopathy, multiple organ dysfunction syndrome, and malignant arrhythmia. In addition, pulmonary edema and carbon monoxide poisoning are caused by chemical agents, gas fumes, and vapors.

INTERVENTIONS

The boy's blood oxygen saturation and blood circulation remained unstable despite various ventilation methods and medications, thus we decided to use ECMO. After 8 days of ECMO support, the patient was successfully weaned from the machine.

OUTCOMES

Under the application of ECMO, the respiratory and circulatory systems significantly improved. Nevertheless, due to the progressive brain injury caused by burns and the poor prognosis, the parents ceased all treatment and the boy passed away.

LESSONS

This case report demonstrates that brain edema and herniation can arise as phenotypes of burn encephalopathy, which is a challenge to treat in children. Children with confirmed or suspected burn encephalopathy should undergo diagnostic tests completed as soon as possible to confirm the diagnosis. After receiving ECMO treatment, the respiratory and circulatory systems of the burn victims reported significantly improved. Hence, ECMO is a viable alternative for supporting patients with burns.

Rat model of smoke inhalation-induced acute lung injury

BACKGROUND

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is a lethal disease with limited therapeutic options and an unacceptably high mortality rate. Understanding the complex pathophysiological processes involved in the development of ALI/ARDS is critical for developing novel therapeutic strategies. Smoke inhalation (SI) injury is the leading cause of morbidity and mortality in patients with burn-associated ALI/ARDS; however, to our knowledge few reliable, reproducible models are available for pure SI animal model to investigate therapeutic options for ALI/ARDS without the confounding variables introduced by cutaneous burn or other pathology.

OBJECTIVE

To develop a small animal model of pure SI-induced ALI and to use this model for eventual testing of novel therapeutics for ALI.

METHODS

Rats were exposed to smoke using a custom-made smoke generator. Peripheral oxygen saturation (SpO₂), heart rate, arterial blood gas, and chest X-ray (CXR) were measured before and after SI. Wet/dry weight (W/D) ratio, lung injury score and immunohistochemical staining of cleaved caspase 3 were performed on harvested lung tissues of healthy and SI animals.

RESULTS

The current study demonstrates the induction of ALI in rats after SI as reflected by a significant, sustained decrease in SpO₂ and the development of diffuse bilateral pulmonary infiltrates on CXR. Lung tissue of animals exposed to SI showed increased inflammation, oedema and apoptosis as reflected by the increase in W/D ratio, injury score and cleaved caspase 3 level of the harvested tissues compared with healthy animals.

CONCLUSION

We have successfully developed a small animal model of pure SI-induced ALI. This model is offered to the scientific community as a reliable model of isolated pulmonary SI-induced injury without the confounding variables of cutaneous injury or other systemic pathology to be used for study of novel therapeutics or other investigation.

Elevated Neuroglobin Lessens Neuroinflammation and Alleviates Neurobehavioral Deficits Induced by Acute Inhalation of Combustion Smoke in the Mouse

Acute inhalation of combustion smoke produces long-term neurologic deficits in survivors. To study the mechanisms that contribute to the development of neurologic deficits and identify targets for prevention, we developed a mouse model of acute inhalation of combustion smoke, which supports longitudinal investigation of mechanisms that underlie the smoke induced inimical sequelae in the brain. Using a transgenic mouse engineered to overexpress neuroglobin, a neuroprotective oxygen-binding globin protein, we previously demonstrated that elevated neuroglobin preserves mitochondrial respiration and attenuates formation of oxidative DNA damage in the mouse brain after smoke exposure. In the current study, we show that elevated neuronal neuroglobin attenuates the persistent inflammatory changes induced by smoke exposure in the mouse brain and mitigates concordant smoke-induced long-term neurobehavioral deficits. Specifically, we found that increases in hippocampal density of GFAP and Iba-1 positive cells that are detected post-smoke in wild-type mice are absent in the neuroglobin overexpressing transgenic (Ngb-tg) mice. Similarly, the smoke induced hippocampal myelin depletion is not observed in the Ngb-tg mice. Importantly, elevated neuroglobin alleviates behavioral and memory deficits that develop after acute smoke inhalation in the wild-type mice. Taken together, our findings suggest that the protective effects exerted by neuroglobin in the brains of smoke exposed mice afford protection from long-term neurologic sequelae of acute inhalation of combustion smoke. Our transgenic mouse provides a tool for assessing the potential of elevated neuroglobin as possible strategy for management of smoke inhalation injury.

Acute inhalation of combustion smoke triggers neuroinflammation and persistent anxiety-like behavior in the mouse

CONTEXT

Acute inhalation of combustion smoke triggers neurologic sequelae in survivors. Due to the challenges posed by heterogeneity of smoke exposures in humans, mechanistic links between acute smoke inhalation and neuropathologic sequelae have not been systematically investigated.

METHODS

Here, using mouse model of acute inhalation of combustion smoke, we studied longitudinal neurobehavioral manifestations of smoke exposures and molecular/cellular changes in the mouse brain.

RESULTS

Immunohistochemical analyses at eight months post-smoke, revealed hippocampal astrogliosis and microgliosis accompanied by reduced myelination. Elevated expression of proinflammatory cytokines was also detected. Longitudinal testing in different neurobehavioral paradigms in the course of post-smoke recovery, revealed lasting anxiety-like behavior. The examined paradigms included the open field exploration/anxiety testing at two, four and six months post-smoke, which detected decreases in total distance traveled and time spent in the central arena in the smoke-exposed compared to sham-control mice, suggestive of dampened exploratory activity and increased anxiety-like behavior. In agreement with reduced open field activity, cued fear conditioning test revealed increased freezing in response to conditioned auditory stimulus in mice after acute smoke inhalation. Similarly, elevated plus maze testing demonstrated lesser presence in open arms of the maze, consistent with anxiety-like behavior, for the post-smoke exposure mice.

CONCLUSIONS

Taken together, our data demonstrate for the first time persistent neurobehavioral manifestations of acute inhalation of combustion smoke and provide new insights into long-term progression of events initiated by disrupted brain oxygenation that might contribute to lasting adverse sequelae in survivors of smoke inhalation injuries.

Animal models of smoke inhalation injury and related acute and chronic lung diseases

Smoke inhalation injury leads to various acute and chronic lung diseases and thus is the dominant cause of fire-related fatalities. In a search for an effective treatment and validation of therapies different classes of animal models have been developed, which include both small and large animals. These models have advanced our understanding of the mechanism of smoke inhalation injury, enabling a better understanding of pathogenesis and pathophysiology and development of new therapies. However, none of the animal models fully mirrors human lungs and their pathologies. All animal models have their limitations in replicating complex clinical conditions associated with smoke inhalation injury in humans. Therefore, for a correct interpretation of the results and to avoid bias, a precise understanding of similarities and differences of lungs between different animal species and humans is critical. We have reviewed and presented comprehensive comparison of different animal models and their clinical relevance. We presented an overview of methods utilized to induce smoke inhalation injuries, airway micro-/macrostructure, advantages and disadvantages of the most commonly used small and large animal models.

Review of the health effects of wildland fire smoke on wildland firefighters and the public

Each year, the general public and wildland firefighters in the US are exposed to smoke from wildland fires. As part of an effort to characterize health risks of breathing this smoke, a review of the literature was conducted using five major databases, including PubMed and MEDLINE Web of Knowledge, to identify smoke components that present the highest hazard potential, the mechanisms of toxicity, review epidemiological studies for health effects and identify the current gap in knowledge on the health impacts of wildland fire smoke exposure. Respiratory events measured in time series studies as incidences of disease-caused mortality, hospital admissions, emergency room visits and symptoms in asthma and chronic obstructive pulmonary disease patients are the health effects that are most commonly associated with community level exposure to wildland fire smoke. A few recent studies have also determined associations between acute wildland fire smoke exposure and cardiovascular health end-points. These cardiopulmonary effects were mostly observed in association with ambient air concentrations of fine particulate matter (PM2.5). However, research on the health effects of this mixture is currently limited. The health effects of acute exposures beyond susceptible populations and the effects of chronic exposures experienced by the wildland firefighter are largely unknown. Longitudinal studies of wildland firefighters during and/or after the firefighting career could help elucidate some of the unknown health impacts of cumulative exposure to wildland fire smoke, establish occupational exposure limits and help determine the types of exposure controls that may be applicable to the occupation.

OXIDATIVE STRESS IN A RAT MODEL OF COTTON SMOKE INHALATION-INDUCED PULMONARY INJURY

BACKGROUND

Smoke inhalation injury refers to airway and lung parenchyma injury and general chemical damage caused by inhaling toxic gases and substances. The aim of this study was to explore the oxidative stress mechanism of cotton smoke inhalation-induced pulmonary injury in a rat model.

MATERIALS AND METHODS

Eighteen male Sprague-Dawley rats were randomly divided into control group, 6 h group, and 24 h group (six rats in each group), which duplicated previous rat cotton smoke-inhalation injury models. Rats in 6 h and 24 h groups were euthanised at 6 h and 24 h after smoke inhalation, respectively. ELISA method was used to detect indicators in the rats' lung tissue. Quantitative iNOS mRNA and γ-GCS mRNA measurements were performed using a fluorescence PCR method.

RESULTS

The concentrations of MDA, NO, iNOS, γ-GCS, iNOS mRNA, and the relative expression of γ-GCS mRNA in the rats' lung tissues in 6 h and 24 h groups were higher than control group (P < 0.05), and the concentration of NO and relative expressions of iNOS mRNA and γ-GCS mRNA in 24 h group were significantly higher than 6 h group (P < 0.05). The concentrations of GSH in 24 h and 6 h groups were significantly lower than control group (P < 0.05), and that in 24 h group was even significantly lower than 6 h group (P < 0.05).

CONCLUSION

In rats with cotton smoke inhalation-induced pulmonary injury, the increased iNOS mRNA transcription can cause increase of iNOS synthesis and promotion of NO synthesis. The increased γ-GCS mRNA transcription can cause increase of γ-GCS synthesis and but decrease of GSH concentration. The activation of the antioxidant system is insufficient to combat oxidative stress damage. So the oxidant/antioxidant system is imbalanced, leading to gradual aggravation of lung injury.

Protective effects of hydrogen sulfide inhalation on oxidative stress in rats with cotton smoke inhalation-induced lung injury

The aim of the present study was to investigate the mechanism by which hydrogen sulfide (H₂S) inhalation protects against oxidative stress in rats with cotton smoke inhalation-induced lung injury. A total of 24 male Sprague-Dawley rats were separated randomly into four groups, which included the control, H₂S, smoke and smoke + H₂S groups. A rat model of cotton smoke inhalation-induced lung injury was established following inhalation of 30% oxygen for 6 h. In addition, H₂S (80 ppm) was inhaled by the rats in the H₂S and smoke + H₂S groups for 6 h following smoke or sham-smoke inhalation. Enzyme-linked immunosorbent assays were performed to measure various indices in the rat lung homogenate, while the levels of nuclear factor (NF)-κBp65 in the lung tissue of the rats were determined and semiquantitatively analyzed using immunohistochemistry. In addition, quantitative fluorescence polymerase chain reaction was employed to detect the mRNA expression of inducible nitric oxide synthase (iNOS) in the rat lung tissue. The concentrations of malondialdehyde (MDA), nitric oxide (NO), inducible iNOS and NF-κBp65, as well as the sum-integrated optical density of NF-κBp65 and the relative mRNA expression of iNOS, in the rat lung tissue from the smoke + H₂S group were significantly lower when compared with the smoke group. The concentrations of MDA, NO, iNOS and NF-κBp65 in the H₂S group were comparable to that of the control group. Therefore, inhalation of 80 ppm H₂S may reduce iNOS mRNA transcription and the production of iNOS and NO in rats by inhibiting NF-κBp65 activation, subsequently decreasing oxidative stress and cotton smoke inhalation-induced lung injury.

Neuroglobin mitigates mitochondrial impairments induced by acute inhalation of combustion smoke in the mouse brain

CONTEXT

Acute inhalation of combustion smoke adversely affects brain homeostasis and energy metabolism. We previously showed that overexpressed neuroglobin (Ngb), neuron specific globin protein, attenuates the formation of smoke inhalation-induced oxidative DNA damage, in vivo, in the mouse brain, while others reported protection by Ngb in diverse models of brain injury, mainly involving oxidative stress and hypoxic/ischemic insults.

OBJECTIVE

To determine to what extent elevated Ngb ameliorates post smoke-inhalation brain bioenergetics and homeostasis in Ngb overexpressing transgenic mouse.

METHODS

Smoke inhalation induced changes in bioenergetics were measured in the wild type and Ngb transgene mouse brain. Modulations of mitochondrial respiration were analyzed using the Seahorse XF24 flux analyzer and changes in cytoplasmic energy metabolism were assessed by measuring enzymatic activities and lactate in the course of post smoke recovery.

RESULTS

Cortical mitochondria from Ngb transgene, better maintained ATP synthesis-linked oxygen consumption and unlike wild type mitochondria did not increase futile oxygen consumption feeding the proton leak, reflecting lesser smoke-induced mitochondrial compromise. Measurements revealed lesser reduction of mitochondrial ATP content and lesser compensatory increases in cytosolic energy metabolism, involving pyruvate kinase and lactate dehydrogenase activities as well as cytosolic lactate levels. Additionally, induction of c-Fos, the early response gene and key neuronal stress sensor, was attenuated in Ngb transgene compared to wild type brain after smoke.

CONCLUSION

Considered together, these differences reflect lesser perturbations produced by acute inhalation of combustion smoke in the Ngb overexpressing mouse, suggesting that Ngb mitigates mitochondrial dysfunction and neurotoxicity and raises the threshold of smoke inhalation-induced brain injury.

Combustion smoke-induced inflammation in the olfactory bulb of adult rats

BACKGROUND

The damaging effect of combustion smoke inhalation on the lung is widely reported but information on its effects on the olfactory bulb is lacking. This study sought to determine the effects of smoke inhalation on the olfactory bulb, whose afferent input neurons in the nasal mucosa are directly exposed to external stimuli, such as smoke.

METHODS

Adult male Sprague-Dawley rats were subjected to combustion smoke inhalation and sacrificed at different time points. Changes in olfactory bulb proteins including vascular endothelial growth factor (VEGF), inducible nitric oxide synthase (iNOS), endothelial nitric oxide synthase (eNOS), neuronal nitric oxide synthase (nNOS), Na+-K+-Cl- cotransporter 1 (NKCC1), glial fibrillary acidic protein (GFAP), and aquaporin-4 (AQP4) were evaluated by Western blot analysis. In addition, ELISA was conducted for cytokine and chemokine levels, and double immunofluorescence labeling was carried out for GFAP/VEGF, GFAP/AQP4, NeuN/nNOS, GFAP/NKCC1, NeuN/NKCC1, GFAP/Rhodamine isothiocyanate (RITC), and transferase dUTP nick end labeling (TUNEL). Aminoguanidine was administered to determine the effects of iNOS inhibition on the targets probed after smoke inhalation.

RESULTS

The results showed a significant increase in VEGF, iNOS, eNOS, nNOS, NKCC1, and GFAP expression in the bulb tissues, with corresponding increases in inflammatory cytokines and chemokines after smoke inhalation. Concurrent to this was a drastic increase in AQP4 expression and RITC permeability. Aminoguanidine administration decreased the expression of iNOS and RITC extravasation after smoke inhalation. This was coupled with a significant reduction in incidence of TUNEL + cells that was not altered with administration of L-NG-nitroarginine methyl ester (L-NAME).

CONCLUSIONS

These findings suggest that the upregulation of iNOS in response to smoke inhalation plays a major role in the olfactory bulb inflammatory pathophysiology, along with a concomitant increase in pro-inflammatory molecules, vascular permeability, and edema. Overall, these findings indicate that the olfactory bulb is vulnerable to smoke inhalation.

Pathophysiology of tobacco smoke exposure: recent insights from comparative and redox proteomics

First-hand and second-hand tobacco smoke are causally linked to a huge number of deaths and are responsible for a broad spectrum of pathologies such as cancer, cardiovascular, respiratory, and eye diseases as well as adverse effects on female reproductive function. Cigarette smoke is a complex mixture of thousands of different chemical species, which exert their negative effects on macromolecules and biochemical pathways, both directly and indirectly. Many compounds can act as oxidants, pro-inflammatory agents, carcinogens, or a combination of these. The redox behavior of cigarette smoke has many implications for smoke related diseases. Reactive oxygen and nitrogen species (both radicals and non-radicals), reactive carbonyl compounds, and other species may induce oxidative damage in almost all the biological macromolecules, compromising their structure and/or function. Different quantitative and redox proteomic approaches have been applied in vitro and in vivo to evaluate, respectively, changes in protein expression and specific oxidative protein modifications induced by exposure to cigarette smoke and are overviewed in this review. Many gel-based and gel-free proteomic techniques have already been used successfully to obtain clues about smoke effects on different proteins in cell cultures, animal models, and humans. The further implementation with other sensitive screening techniques could be useful to integrate the comprehension of cigarette smoke effects on human health. In particular, the redox proteomic approach may also help identify biomarkers of exposure to tobacco smoke useful for preventing these effects or potentially predictive of the onset and/or progression of smoking-induced diseases as well as potential targets for therapeutic strategies.

Overexpressed neuroglobin raises threshold for nitric oxide-induced impairment of mitochondrial respiratory activities and stress signaling in primary cortical neurons

Surges of nitric oxide compromise mitochondrial respiration primarily by competitive inhibition of oxygen binding to cytochrome c oxidase (complex IV) and are particularly injurious in neurons, which rely on oxidative phosphorylation for all their energy needs. Here, we show that transgenic overexpression of the neuronal globin protein, neuroglobin, helps diminish protein nitration, preserve mitochondrial function and sustain ATP content of primary cortical neurons challenged by extended nitric oxide exposure. Specifically, in transgenic neurons, elevated neuroglobin curtailed nitric oxide-induced alterations in mitochondrial oxygen consumption rates, including baseline oxygen consumption, consumption coupled with ATP synthesis, proton leak and spare respiratory capacity. Concomitantly, activation of genes involved in sensing and responding to oxidative/nitrosative stress, including the early-immediate c-Fos gene and the phase II antioxidant enzyme, heme oxygenase-1, was diminished in neuroglobin-overexpressing compared to wild-type neurons. Taken together, these differences reflect a lesser insult produced by similar concentrations of nitric oxide in neuroglobin-overexpressing compared to wild-type neurons, suggesting that abundant neuroglobin buffers nitric oxide and raises the threshold of nitric oxide-mediated injury in neurons.

Mitochondrial dysfunction, oxidative stress, and major depressive disorder

There is controversy about depression being a physical illness, in part because a reproducible, sensitive, and specific biologic marker is not available. However, there is evidence that mitochondrial dysfunction and oxidative stress may be associated with abnormal brain function and mood disorders, such as depression. This paper reviews selected human and animal studies providing evidence that intracellular mitochondrial metabolic dysfunction in specific brain regions is associated with major depressive disorder. This supports the hypothesis that chronic mitochondrial dysfunction in specific tissues may be associated with depression. Evaluation of mitochondrial dysfunction in specific tissues may broaden the perspective of depression beyond theories about neurotransmitters or receptor sites, and may explain the persistent signs and symptoms of depression.

Assessment of lung inflammation in a mouse model of smoke inhalation and burn injury: strain-specific differences

ABSTRACT To test concepts developed in our ovine model of acute respiratory distress syndrome, specifically the roles of neuropeptides and other peptide mediators, a recently developed murine model of combined smoke inhalation and burn (SB) injury was extended by applying methods for quantitative assessment of acute inflammation in the lung. Mice received SB injury per protocol, n = 5 to 7 per group. Mice were anesthetized with i.p. ketamine/xylazine, endotracheally intubated, and exposed to cooled cotton smoke (4 x 30 sec for Balb/C, 2 x 30 sec for C57BL/6). After s.c. injection of 1 mL 0.9% saline, each received a 40% total body surface area (TBSA) flame burn. Buprenorphine (0.1 mg/kg) was given i.p. for postoperative analgesia; 0.9% saline was given i.p. at 4 mL/kg per %TBSA burn. Evans Blue dye (EB) was injected i.v. 15 min before sacrifice. Lung wet/dry weight ratio was measured. In other animals, after vascular perfusion with buffered saline, lungs were sampled and analyzed for myeloperoxidase (MPO), using an EIA kit, and for their content of EB dye. There was a significant (p < 0.05) increase in EB dye content, wet/dry weight ratio, and MPO 24 h after injury in Balb/C mice. Similar increases were seen in C57BL/6 mice 48 h after SB injury, but not at 24 h. C57 mice tolerated less smoke inhalation than Balb/C mice, due to postexposure apnea, and required 48 h to show significant increases in these variables. Direct comparison between animals injured by 40% TBSA burn and 2 x 30 sec smoke exposure and sacrificed after 48 h showed significantly greater abnormality in the C57BL/6 mice. The mouse model can be used effectively to assess acute inflammation in the lung.

Carbon monoxide-sensitive apoptotic death of erythrocytes

Carbon monoxide (CO) intoxication severely interferes with the oxygen-transporting function of haemoglobin. Beyond that, CO participates in the regulation of apoptosis. CO could be generated from CO-releasing molecules (CORM), such as the tricarbonyl-dichlororuthenium (II) dimer (CORM-2), which is presently considered for the treatment of vascular dysfunction, inflammation, tissue ischaemia and organ rejection. CORM-2 is at least partially effective by modifying gene expression and mitochondrial potential. Erythrocytes lack nuclei and mitochondria but may undergo suicidal cell death or eryptosis, characterized by cell shrinkage and phospholipid scrambling of the cell membrane. Eryptosis is triggered by the increase in cytosolic Ca²⁺ activity ([Ca²⁺](i)). The present study explored whether CORM-2 influences eryptosis. To this end, [Ca²⁺](i) was estimated from Fluo-3-fluorescence, cell volume from forward scatter, phospholipid scrambling from annexin-V-binding and haemolysis from haemoglobin release. CO-binding haemoglobin (COHb) was estimated utilizing a blood gas analyser. As a result, exposure of erythrocytes for 24 hr to CORM-2 (≥5 μM) significantly increased COHb, [Ca²⁺](i) , forward scatter, annexin-V-binding and haemolysis. Annexin-V-binding was significantly blunted by 100% oxygen and was virtually abolished in the nominal absence of Ca²⁺. In conclusion, CORM-2 stimulates cell membrane scrambling of erythrocytes, an effect largely due to Ca²⁺ entry and partially reversed by O₂.

Transgenic overexpression of neuroglobin attenuates formation of smoke-inhalation-induced oxidative DNA damage, in vivo, in the mouse brain

Acute inhalation of combustion smoke causes neurological deficits in survivors. Inhaled smoke includes carbon monoxide, noxious gases, and a hypoxic environment, which disrupt oxygenation and generate free radicals. To replicate a smoke-inhalation scenario, we developed an experimental model of acute exposure to smoke for the awake mouse/rat and detected induction of biomarkers of oxidative stress. These include inhibition of mitochondrial respiratory complexes and formation of oxidative DNA damage in the brain. DNA damage is likely to contribute to neuronal dysfunction and progression of brain injury. In the search for strategies to attenuate the smoke-initiated brain injury, we produced a transgenic mouse overexpressing the neuronal globin protein neuroglobin. Neuroglobin was neuroprotective in diverse models of ischemic/hypoxic/toxic brain injuries. Here, we report lesser inhibition of respiratory complex I and reduced formation of smoke-induced DNA damage in neuroglobin transgenic compared to wild-type mouse brain. DNA damage was assessed using the standard comet assay, as well as a modified comet assay done in conjunction with an enzyme that excises oxidized guanines that form readily under conditions of oxidative stress. Both comet assays revealed that overexpressed neuroglobin attenuates the formation of oxidative DNA damage, in vivo, in the brain. These findings suggest that elevated neuroglobin exerts neuroprotection, in part, by decreasing the impact of acute smoke inhalation on the integrity of neuronal DNA.

Differential inhibition of mitochondrial respiratory complexes by inhalation of combustion smoke and carbon monoxide, in vivo, in the rat brain

Combustion smoke contains gases and particulates, which act via hypoxia and cytotoxicity producing mechanisms to injure cells and tissues. While carbon monoxide (CO) is the major toxicant in smoke, its toxicity is exacerbated in the presence of other compounds. Here, we examined modulations of mitochondrial and cytosolic energy metabolism by inhalation of combustion smoke versus CO, in vivo, in the rat brain. Measurements revealed reduced activities of respiratory chain (RC) complexes, with greater inhibition by smoke than equivalent CO in ambient air. In the case of RC complex IV, inhibition by CO and smoke was similar--suggesting that complex IV inhibition is primarily by the action of CO. In contrast, inhibition of complexes I and III was greater by smoke. Increases in cytosolic lactate dehydrogenase and pyruvate kinase activities accompanied inhibition of RC complexes, likely reflecting compensatory increases in cytosolic energy production. Together, the data provide new insights into the mechanisms of smoke inhalation-induced perturbations of brain energetics, which impact neuronal function and contribute to the development of neuropathologies in survivors of exposures to CO and combustion smoke.

Neuroglobin, cytoglobin, and transcriptional profiling of hypoxia-related genes in the rat cerebellum after prenatal chronic very mild carbon monoxide exposure (25 ppm)

The expression of neuroglobin (Ngb) and cytoglobin (Cygb), two recently discovered globins with a potential neuroprotective activity against hypoxia and oxidative stress, was investigated in the cerebellum of young rats (postnatal day 20) after being exposed to chronic mild carbon monoxide (CO) at 25 ppm during prenatal (group A), prenatal and postnatal (group B), the postnatal period only (group C), and air (group D). The expression of genes associated with hypoxia signaling pathways was also investigated in the rat cerebella by real-time RT-PCR after CO exposure. Ngb and Cygb mRNAs did not change in any CO-exposed group. Quantitative immunohistochemistry showed no significant change in Ngb protein; however, there was a significant increase of Cygb protein in rats from groups A, B, and C when compared with group D. In group B, genes related to the generation of reactive oxygen species (Nos2) and lipid metabolism (Apat2) were upregulated. In contrast, no changes were found in the expression of 8 genes typically upregulated by hypoxic conditions (Angptl4, Arnt2, Casp1, Crebbp, Hif1a, Hif3a, Mt3, or Vegfa) in any CO-exposed group, suggesting that hypoxia-related gene expression is not altered by this mild CO exposure. Cygb but not Ngb may protect cerebellar cells from the chronic presence of CO exposure during prenatal and postnatal development.

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.

Accumulation of oxidatively generated DNA damage in the brain: a mechanism of neurotoxicity

Unrepaired or erroneously repaired DNA lesions drive genomic instability and contribute to cellular and organ decline. Since delayed neuropathologies are common in survivors of smoke inhalation injuries, we asked whether the integrity of brain DNA might be compromised by acute exposure to combustion smoke. Although many studies demonstrate that the brain is equipped to repair oxidatively damaged DNA, to date, the capacity for accurate DNA repair under conditions of disrupted oxygenation and oxidative stress has not been defined. We show that DNA adducts detectable by their ability to block PCR amplification form in the rat hippocampus after acute exposure to smoke. To identify the different types of adducts and to dissect their temporal formation and repair profiles in vivo in the brain, we used DNA-modifying enzymes to convert specific adducts into strand breaks prior to PCR amplification. Using this strategy, we detected formation of oxidative DNA adducts early on after smoke inhalation, while mismatched bases emerged at the later recovery times, potentially due to an erroneous DNA repair process. Erroneous repair can be mutagenic and because the initial smoke-induced oxidative damage to DNA is extensive, compromised fidelity of DNA repair may underlie neurotoxicity and contribute to delayed death of hippocampal neurons.

Long term environmental tobacco smoke activates nuclear transcription factor-kappa B, activator protein-1, and stress responsive kinases in mouse brain

Environmental tobacco smoke (ETS) is a key mediator of several diseases. Tobacco smoke contains a mixture of over 4700 chemical components many of which are toxic and have been implicated in the etiology of oxidative stress related diseases such as chronic obstructive pulmonary disease, Parkinson's disease, asthma, cancer and cardiovascular disease. However, the mechanism of action of cigarette smoke in the onset of these diseases is still largely unknown. Previous studies have revealed that the free radicals generated by cigarette smoke may contribute to many of these chronic health problems and this study sought to address the role of environmental tobacco smoke in oxidative stress related damage in different regions of the mouse brain. In this study, male mice were exposed for 7h/day, 7 days/week, for 6 months. Our results show that tobacco smoke led to increased generation of reactive oxygen species with an increase in NF-kappaB activation. Gel shift analysis also revealed the elevated level of the oxidative stress sensitive proinflammatory nuclear transcription factor-kappa B and activator protein-1 in different regions of the brain of cigarette smoke exposed mice. Tobacco smoke led to activation of COX-2 in all the regions of the brain. Activation of mitogen activated protein kinase and c-Jun N-terminal kinase were also observed in various regions of brain of ETS exposed mice. Overall our results indicate that exposure to long-term cigarette smoke induces oxidative stress leading to activation of stress induced kinases and activation of proinflammatory transcription factors.