Dibutyryl cAMP, aminophylline, and beta-adrenergic agonists protect against pulmonary edema caused by phosgene

Evaluation of an in vitro screening model to assess phosgene inhalation injury

Therapeutic development against exposure to toxic gases is hindered by the lack of appropriate models to evaluate candidate compounds prior to animal efficacy studies. In this study, an in vitro, air-liquid interface exposure model has been tested to examine its potential application for screening treatments for phosgene (carbonyl chloride)-induced pulmonary injury. Epithelial cultures on Transwell^® inserts, combined with a Vitrocell^® exposure apparatus, provided a physiologically relevant exposure environment. Differentiated human bronchial epithelial (16HBE) cultures were exposed for 8 min to phosgene ranging from 0 to 64 ppm and assessed for changes in transepithelial electrical resistance (TEER, epithelial barrier integrity), cellular viability (XTT) and post-exposure (PE) cellular metabolic energy status. Exposure to phosgene concentrations ≥8 ppm caused dose-dependent and significant decreases in TEER and XTT which did not recover within 24-h PE. In addition, at 64 ppm the rate of oxidative glutamine metabolism was significantly inhibited at 6 and 24 h after exposure. Glycolytic activities (glucose utilization and lactate production) were also inhibited, but to a lesser extent. Decreased glycolytic function can translate to insufficient energy sources to counteract barrier function failure. Consistent and sensitive markers of phosgene exposure were TEER, cell viability and decreased metabolism. As such, we have assessed an appropriate in vitro model of phosgene inhalation that produced quantifiable alterations in markers of lung cell metabolism and injury in human airway epithelial cells. Data indicate the suitability of this model for testing classes of anti-edemagenic compounds such as corticosteroids or phosphodiesterase inhibitors for evaluating phosgene therapeutics.

Conceptual approaches for treatment of phosgene inhalation-induced lung injury

Toxic industrial chemicals are used throughout the world to produce everyday products such as household and commercial cleaners, disinfectants, pesticides, pharmaceuticals, plastics, paper, and fertilizers. These chemicals are produced, stored, and transported in large quantities, which poses a threat to the local civilian population in cases of accidental or intentional release. Several of these chemicals have no known medical countermeasures for their toxic effects. Phosgene is a highly toxic industrial chemical which was used as a chemical warfare agent in WWI. Exposure to phosgene causes latent, non-cardiogenic pulmonary edema which can result in respiratory failure and death. The mechanisms of phosgene-induced pulmonary injury are not fully identified, and currently there is no efficacious countermeasure. Here, we provide a proposed mechanism of phosgene-induced lung injury based on the literature and from studies conducted in our lab, as well as provide results from studies designed to evaluate survival efficacy of potential therapies following whole-body phosgene exposure in mice. Several therapies were able to significantly increase 24h survival following an LCt50-70 exposure to phosgene; however, no treatment was able to fully protect against phosgene-induced mortality. These studies provide evidence that mortality following phosgene toxicity can be mitigated by neuro- and calcium-regulators, antioxidants, phosphodiesterase and endothelin receptor antagonists, angiotensin converting enzymes, and transient receptor potential cation channel inhibitors. However, because the mechanism of phosgene toxicity is multifaceted, we conclude that a single therapeutic is unlikely to be sufficient to ameliorate the multitude of direct and secondary toxic effects caused by phosgene inhalation.

Phosgene exposure: a case of accidental industrial exposure

INTRODUCTION

Phosgene is a rare exposure with strong clinical implications. We report a phosgene exposure that resulted in the patient's death.

CASE REPORT

A 58 year-old man arrived to the emergency department 1 hour after exposure to phosgene with complaints of a sore throat. Initial vital signs were blood pressure 175/118 mmHg, heart rate 98/min, respirations 12/min, and oxygen saturation of 93% on room air. Physical exam revealed few scattered rhonchi, without signs of distress. Initial arterial blood gases (ABG's) revealed pH 7.42, pCO2 43 mmHg, pO2 68 mmHg, HCO3 27 meq/L, and oxygen saturation of 93% on room air. Initial chest x-ray 2 hours after the exposure demonstrated clear lung fields. Approximately 2.5 hours after the exposure, he began complaining of dyspnea, restlessness and his oxygen saturation dropped below 90%. He received nebulized albuterol, 1 gram intravenous methylprednisolone, and 100 % oxygen via face mask. Minimal improvement was noted and he was intubated. The post intubation chest x-ray, 3.5 hours after the exposure, revealed diffuse alveolar infiltrates. Acetylcysteine, terbutaline, and IV steroids were administered without improvement. The patient died 30 hours after exposure.

DISCUSSION

There are many misunderstandings concerning phosgene due to its rare presentation. Traditional treatment modalities are often unproven in human trials and were unsuccessful in this case.

CONCLUSION

This case highlights the significant toxicity that results from phosgene exposure and the challenges of the limited treatment modalities. There is concern for the use of this agent in chemical terrorism.

Defining the phosphodiesterase superfamily members in rat brain microvessels

Eleven phosphodiesterase (PDE) families are known, each having several different isoforms and splice variants. Recent evidence indicates that expression of individual PDE family members is tissue-specific. Little is known concerning detailed PDE component expression in brain microvessels where the blood-brain-barrier and the local cerebral blood flow are thought to be regulated by PDEs. The present study attempted to identify PDE family members that are expressed in brain microvessels. Adult male F344 rats were sacrificed and blocks of the cerebral cortex and infratentorial areas were dissected. Microvessels were isolated using a filtration method, and total RNA was extracted. RNA quality and quantity were determined using an Agilent bioanalyzer. The isolated cortical and infratentorial microvessel total RNA amounts were 2720 ± 750 ng (n = 2) and 250 ± 40 ng (n = 2), respectively. Microarrays with 22 000 transcripts demonstrated that there were 16 PDE transcripts in the PDE superfamily, exhibiting quantifiable density in the microvessels. An additional immunofluorescent study verified that PDE4D (cAMP-specific) and PDE5A (cGMP-specific) were colocalized with RECA-1 (an endothelial marker) in the cerebral cortex using both F344 rats and Sprague-Dawley rats (n = 3-6/strain). In addition, PDE4D and PDE5A were found to be colocalized with alpha-smooth muscle actin which delineates cerebral arteries and arterioles as well as pericytes. In conclusion, a filtration method followed by microarray analyses allows PDE components to be identified in brain microvessels, and confirmed that PDE4D and PDE5A are the primary forms expressed in rat brain microvessels.

Toxic effects following phosgene exposure of human epithelial lung cells in vitro using a CULTEX® system

The aim of the present study was to investigate toxic effects following phosgene exposure of human epithelial lung cells (A549) in vitro using a CULTEX® system. In particular, toxic effects regarding early biomarkers emerging during the latency period following exposure might be of great value for medical treatment. Cells cultured on semi-permeable membranes were directly exposed at the liquid-air interface to different concentrations of phosgene, or dry medical air. Cell membrane integrity (leakage of LDH), metabolic activity (reduction of Alamar Blue), oxidative damage (GSH, and HO-1, in cell lysates), and release of IL-8, were studied. For most of the above-mentioned biological end-point markers, significant changes could be assessed following a 20 min exposure to 1.0 ppm and 2.0 ppm phosgene. Moreover, except for IL-8, all biological marker profiles showed to be in line with results obtained by others in animal studies. The C×t value of 40 ppm min appeared to be constant. The overall results suggest that at 4 h post-exposure a maximal level of toxicity was achieved. Our results demonstrate the suitability of a CULTEX® system to detect toxic effects induced by phosgene on human epithelial lung cells, which may contribute to the discovery of early biomarkers for new medical countermeasures.

Management of phosgene-induced acute lung injury

CONTEXT

Phosgene is a substance of immense importance in the chemical industry. Because of its widespread industrial use, there is potential for small-scale exposures within the workplace, large-scale accidental release, or even deliberate release into a built-up area.

OBJECTIVE

This review aims to examine all published studies concerning potential treatments for phosgene-induced acute lung injury and incorporate them into up-to-date clinical guidance. In addition, it aims to contrast the approaches when dealing with small numbers of patients known to be exposed (possibly with dose information) with the presentation of a large and heterogeneous population of casualties following a significant industrial accident or deliberate release; no published guidelines have specifically addressed this second problem.

METHODS

PubMed and Embase were searched for all available years till April 2010 and 584 papers were identified and considered.

EXPERIMENTAL STUDIES

Because of the nature of the injury, there have been no human trials of patients exposed to phosgene. Multiple small and large animal studies have been performed to examine potential treatments of phosgene-induced acute lung injury, but many of these used isolated organ models, pretreatment regimens, or clinically improbable doses. Recent studies in large animals using both realistic time frames and dosing regimens have improved our knowledge, but clinical guidance remains based on incomplete data. Management of a small-scale, confirmed exposure. In the circumstance of a small-scale, confirmed industrial release where a few individuals are exposed and present rapidly, an intravenous bolus of high-dose corticosteroid (e.g., methylprednisolone 1 g) should be considered, although there are no experimental data to support this recommendation. The evidence is that there is no benefit from nebulized steroid even when administered 1 h after exposure, or methylprednisolone if administered intravenously ≥6 h after exposure. Consideration should also be given to administration of nebulized acetylcysteine 1-2 g, though there is no substantive evidence of benefit outside a small animal, isolated lung model and there is a possibility of adverse effects. If the oxygen saturation falls below 94%, patients should receive the lowest concentration of supplemental oxygen to maintain their SaO(2) in the normal range. Once patients require oxygen, nebulized β-agonists [e.g., salbutamol (albuterol) 5 mg by nebulizer every 4 h] may reduce lung inflammation if administered within 1 h of exposure. Elective intubation should be considered early using an ARDSnet protective ventilation strategy. Management of a large-scale, non-confirmed exposure. In the circumstances of a large-scale industrial or urban release, not all patients presenting will have been exposed and health services are likely to be highly stretched. In this situation, patients should not be treated immediately as there is no evidence that delaying therapy causes harm, rather they should be rested and observed with regular physical examination and measurement of peripheral oxygen saturations. Once a patient's oxygen saturation falls below 94%, treatment with the lowest concentration of oxygen required to maintain their oxygen saturations in the normal range should be started. Once oxygen has been started, nebulized β-agonists [e.g., salbutamol (albuterol) 5 mg by nebulizer every 4 h] may reduce lung inflammation if administered within 1 h of exposure, though delayed administration which is likely following a large-scale release has not been tested formally. There is no benefit from nebulized steroid even when administered 1 h after exposure, or high-dose corticosteroid if administered intravenously ≥6 h after exposure. Although there are no experimental data to support this recommendation, an intravenous bolus of high-dose corticosteroid (e.g., methylprednisolone 1 g) may be considered if presentation is <6 h and resources allow. Depending on the numbers of casualties presenting, invasive ventilation should be initiated either electively once symptoms present (especially where there is a short latent period, indicating likelihood of more significant injury), or delayed until required. Ventilation should be with high positive end expiratory pressure, ARDSnet recommended ventilation.

CONCLUSIONS

The mechanisms underlying the phosgene-induced acute lung injury are not well understood. Future experimental work should ensure that potential treatments are tested in a large animal model using realistic dosing regimens and clinically relevant timings, such as those that might be found in a mass casualty situation.

Therapeutic Treatments of Phosgene-Induced Lung Injury

A series of studies was performed to address treatment against the former chemical warfare edemagenic gas phosgene. Both in situ and in vivo models were used to assess the efficacy of postexposure treatment of phosgene-induced lung injury using clinically existing drugs. The degree of efficacy was judged by examining treatment effects on pulmonary edema formation (PEF) as measured by wet/dry weight (WW/DW) ratios, real-time (in situ) lung weight gain (LWG), survival rates (SR), odds ratios, and glutathione (GSH) redox states. Drugs included N-acetylcysteine (NAC), ibuprofen (IBU), aminophylline (AMIN), and isoproterenol (ISO). Using the in situ isolated perfused rabbit lung model (IPRLM), intratracheal (IT) NAC (40 mg/kg bolus) delivered 45-60 min after phosgene exposure (650 mg/m(3)) for10 min lowered pulmonary artery pressure, LWG, leukotrienes (LT) C(4)/D(4)/E(4), lipid peroxidation, and oxidized GSH. We concluded that NAC protected against phosgene-induced lung injury by acting as an antioxidant by maintaining protective levels of GSH, reducing both lipid peroxidation and production of arachidonic acid metabolites. Also in IPRLM, administration of AMIN (30 mg/kg) 80-90 min after phosgene exposure significantly reduced lipid peroxidation and perfusate LTC(4)/D(4)/E(4), reduced LWG, and prevented phosgene-induced decreases in lung tissue cAMP. These data suggest that protective mechanisms observed with AMIN involve decreased LTC(4)/D(4)/E(4) mediated pulmonary capillary permeability and attenuated lipid peroxidation. Direct antipermeability effects of AMIN-induced upregulation of cAMP on cellular contraction may also be important in protection against phosgene-induced lung injury. Posttreatment with ISO in the IPRLM by either combined intravascular (iv; infused into pulmonary artery at 24 microg/min infused) + IT (24 microg bolus) or IT route alone 50-60 min after phosgene exposure significantly lowered pulmonary artery pressure, tracheal pressure, and LWG. ISO treatment significantly enhanced GSH products or maintained protective levels when compared with results from phosgene-exposed only rabbits. These data suggest that protective mechanisms for ISO involve reduction in vascular pressure, decreased LTC(4)/D(4)/E(4)-mediated pulmonary capillary permeability, and favorably maintained lung tissue GSH redox states. For in vivo male mouse (CD-1, 25-30 g) studies IBU was administered ip within 20 min after a lethal dose of phosgene (32 mg/m(3) for 20 min) at 0 (saline), 3, 9, or 15 mg/mouse. Five hours later, a second IBU injection was given but at half the original doses (0, 1.5, 4.5, and 7.5 mg/mouse); therefore, these treatment groups are now referred to as the 0/0, 3/1.5, 9/4.5, and 15/7.5 mg IBU/mouse groups. SRs and odds ratios were calculated for each dose at 12 and 24 h. The 12-h survival was 63% for 9/4.5 mg IBU and 82% for the 15/7.5 mg IBU groups, compared with 25% for saline-treated phosgene-exposed mice. At 24 h, those survival rates were reduced to 19%, 19%, and 6%, respectively. In the 15/7.5 mg IBU group, lung WW/DW ratios were significantly lower than in saline-treated mice at 12 h. Lipid peroxidation was lower only for the 9/4.5 mg IBU dose; however, nonprotein sulfhydryls (a measure of GSH) were greater across all IBU doses. The odds ratio was 5 for the 9/4.5 IBU group at 12 h and 13 for the 15/7.5 mg IBU group, compared with 3.5 for both groups at 24 h. IBU posttreatment increased the survival of mice at 12 h by reducing PEF, lipid peroxidation, and GSH depletion. In conclusion, effective treatment of phosgene-induced lung injury involves early postexposure intervention that could reduce free radical species responsible for lipid peroxidation, correct the imbalance in the GSH redox state, and prevent the release of biological mediators such as leukotrienes, which are accountable for increased permeability.

Workshop Summary: Phosgene-Induced Pulmonary Toxicity Revisited: Appraisal of Early and Late Markers of Pulmonary Injury From Animal Models With Emphasis on Human Significance

A workshop was held February 14, 2007, in Arlington, VA, under the auspices of the Phosgene Panel of the American Chemistry Council. The objective of this workshop was to convene inhalation toxicologists and medical experts from academia, industry and regulatory authorities to critically discuss past and recent inhalation studies of phosgene in controlled animal models. This included presentations addressing the benefits and limitations of rodent (mice, rats) and nonrodent (dogs) species to study concentration x time (C x t) relationships of acute and chronic types of pulmonary changes. Toxicological endpoints focused on the primary pulmonary effects associated with the acute inhalation exposure to phosgene gas and responses secondary to injury. A consensus was reached that the phosgene-induced increased pulmonary extravasation of fluid and protein can suitably be probed by bronchoalveolar lavage (BAL) techniques. BAL fluid analyses rank among the most sensitive methods to detect phosgene-induced noncardiogenic, pulmonary high-permeability edema following acute inhalation exposure. Maximum protein concentrations in BAL fluid occurred within 1 day after exposure, typically followed by a latency period up to about 15 h, which is reciprocal to the C x t exposure relationship. The C x t relationship was constant over a wide range of concentrations and single exposure durations. Following intermittent, repeated exposures of fixed duration, increased tolerance to recurrent exposures occurred. For such exposure regimens, chronic effects appear to be clearly dependent on the concentration rather than the cumulative concentration x time relationship. The threshold C x t product based on an increased BAL fluid protein following single exposure was essentially identical to the respective C x t product following subchronic exposure of rats based on increased pulmonary collagen and influx of inflammatory cells. Thus, the chronic outcome appears to be contingent upon the acute pulmonary threshold dose. Exposure concentrations high enough to elicit an increased acute extravasation of plasma constituents into the alveolus may also be associated with surfactant dysfunction, intra-alveolar accumulation of fibrin and collagen, and increased recruitment and activation of inflammatory cells. Although the exact mechanisms of toxicity have not yet been completely elucidated, consensus was reached that the acute pulmonary toxicity of phosgene gas is consistent with a simple, irritant mode of action at the site of its initial deposition/retention. The acute concentration x time mortality relationship of phosgene gas in rats is extremely steep, which is typical for a local, directly acting pulmonary irritant gas. Due to the high lipophilicity of phosgene gas, it efficiently penetrates the lower respiratory tract. Indeed, more recent published evidence from animals or humans has not revealed appreciable irritant responses in central and upper airways, unless exposure was to almost lethal concentrations. The comparison of acute inhalation studies in rats and dogs with focus on changes in BAL fluid constituents demonstrates that dogs are approximately three to four times less susceptible to phosgene than rats under methodologically similar conditions. There are data to suggest that the dog may be useful particularly for the study of mechanisms associated with the acute extravasation of plasma constituents because of its size and general morphology and physiology of the lung as well as its oronasal breathing patterns. However, the study of the long-term sequelae of acute effects is experimentally markedly more demanding in dogs as compared to rats, precluding the dog model to be applied on a routine base. The striking similarity of threshold concentrations from single exposure (increased protein in BAL fluid) and repeated-exposure 3-mo inhalation studies (increased pulmonary collagen deposition) in rats supports the notion that chronic changes depend on acute threshold mechanisms.

Clinical management of casualties exposed to lung damaging agents: a critical review

There is no specific antidote for the treatment of casualties exposed to chlorine, phosgene, or mustards; therefore, management is largely supportive. Corticosteroid treatment has been given to casualties accidentally exposed to chlorine. Clinical data on efficacy are inconclusive as the numbers given steroids have been small and the indications for administration unclear. There have been no clinical controlled studies. There is a stronger evidence base from animal studies, particularly from porcine and rodent models. Lung injury induced by phosgene and mustard appears to be mediated by glutathione depletion, lipid peroxidation, free radical generation, and subsequent cellular toxicity. There is limited evidence to suggest that repletion of glutathione reduces and/or prevents lung damage by these agents. This may provide an opportunity for therapeutic intervention.

Microbiological, biological, and chemical weapons of warfare and terrorism

Microbiological, biological, and chemical toxins have been employed in warfare and in terrorist attacks. In this era, it is imperative that health care providers are familiar with illnesses caused by these agents. Botulinum toxin produces a descending flaccid paralysis. Staphylococcal enterotoxin B produces a syndrome of fever, nausea, and diarrhea and may produce a pulmonary syndrome if aerosolized. Clostridium perfringens epsilon-toxin could possibly be aerosolized to produce acute pulmonary edema. Ricin intoxication can manifest as gastrointestinal hemorrhage after ingestion, severe muscle necrosis after intramuscular injection, and acute pulmonary disease after inhalation. Nerve agents inhibit acetylcholinesterase and thus produce symptoms of increased cholinergic activity. Ammonia, chlorine, vinyl chloride, phosgene, sulfur dioxide, and nitrogen dioxide, tear gas, and zinc chloride primarily injure the upper respiratory tract and the lungs. Sulfur mustard (and nitrogen mustard) are vesicant and alkylating agents. Cyanide poisoning ranges from sudden-onset headache and drowsiness to severe hypoxemia, cardiovascular collapse, and death. Health care providers should be familiar with the medical consequences of toxin exposure, and understand the pathophysiology and management of resulting illness.

Acute changes in lung histopathology and bronchoalveolar lavage parameters in mice exposed to the choking agent gas phosgene

Phosgene (CG) is a highly irritant gas widely used industrially as a chemical intermediate for the production of dyes, pesticides, and plastics, and can cause life-threatening pulmonary edema within 24 hours of exposure. This study was designed to investigate acute changes in lung tissue histopathology and selected bronchoalveolar lavage fluid (BALF) factors over time to determine early diagnostic indicators of exposure. Three groups of 40 male mice each were exposed to 32 mg/m3 (8 ppm) CG for 20 minutes, and 3 groups of 40 control male mice were exposed to filtered room air for 20 minutes, both exposures were followed by room air washout for 5 minutes. At 1, 4.8, 12, 24, 48, and 72 hours after exposure each group of mice was euthanized and processed for histopathology, bronchoalveolar lavage or gravimetric measurements, respectively. Over time, the histopathological lesions were characterized by acute changes consisting of alveolar and interstitial edema, fibrin and hemorrhage, followed by significant alveolar and interstitial flooding with inflammatory cell infiltrates and scattered bronchiolar and terminal airway epithelial degeneration and necrosis. From 48 to 72 hours, there was partial resolution of the edema and degenerative changes, followed by epithelial and fibroblastic regeneration centered on the terminal bronchiolar areas. Bronchoalveolar lavage was processed for cell differential counts, LDH, and protein determination. Comparative analysis revealed significant increases in both postexposure lung wet/dry weight ratios, and early elevations of BALF LDH and protein, and later elevations in leukocytes. This article describes the use of histopathology to chronicle the temporal pulmonary changes subsequent to whole body exposure to phosgene, and correlate these changes with BALF ingredients and postexposure lung wet weights in an effort to characterize toxic gas-induced acute lung injury and identify early markers of phosgene exposure.

Regulation of cyclic AMP in rat pulmonary microvascular endothelial cells by rolipram-sensitive cyclic AMP phosphodiesterase (PDE4)

We report here studies on the regulation of the metabolism of adenosine 3',5'-monophosphate (cAMP) in established and primary cultures of rat pulmonary microvascular endothelial cells (RPMVEC). Inhibition by rolipram, a selective inhibitor of cAMP phosphodiesterase (PDE) of the PDE4 gene family, was required to achieve maximal cAMP accumulation induced by direct or receptor-mediated adenylate cyclase activation when measured by [3H]-adenine prelabeling. Rolipram increased cAMP accumulation more effectively than did forskolin, isoproterenol, or adenosine derivatives alone, although extensive synergy was seen with combined agents. High-affinity PDE4 inhibitors, but not low-affinity or non-selective inhibitors, were effective inducers of cAMP accumulation in intact cells. The maximum effects (i.e. intrinsic activities) of these agents in the intact cell did not correlate with their in vitro PDE4 inhibitory affinities. RPMVEC were shown to express almost exclusively the PDE4 gene family isoforms A6 and B3. Guanosine 3',5'-monophosphate hydrolysis, observed in other types of endothelial cells was not found in early or late passage RPMVEC. Reverse transcription-polymerase chain reaction identification of mRNAse supported these conclusions with the exception that PDE2 and PDE4D mRNA isoform transcripts were present. These studies also support the conclusion that the mechanism of rolipram reversal of rat lung ischemia-reperfusion-induced permeability involves PDE4 inhibition in the microvascular endothelial cells of the lung.

Phosgene exposure: mechanisms of injury and treatment strategies

Phosgene (carbonyl chloride, CAS 75-44-5) is a highly reactive gas of historical interest and current industrial importance. Phosgene has also proved to be a useful model for the study of those biochemical mechanisms that lead to permeability-type pulmonary edema (adult respiratory distress syndrome). In turn, the study of phosgene-induced adult respiratory distress syndrome has provided insights leading to revised treatment strategies for exposure victims. We summarized recent findings on the mechanisms of phosgene-induced pulmonary edema and their implications for victim management. In light of that research, we also provide a comprehensive approach to the management and treatment of phosgene exposure victims.

Effect of dietary treatment with n-propyl gallate or vitamin E on the survival of mice exposed to phosgene

Phosgene, widely used in industrial processes, can cause life-threatening pulmonary edema and acute lung injury. One mechanism of protection against phosgene-induced lung injury may involve the use of antioxidants. The present study focused on dietary supplementation in mice using n-propyl gallate (nPG)--a gallate acid ester compound used in food preservation--and vitamin E. Five groups of male mice were studied: group 1, control-fed with Purina rodent chow 5002; group 2, fed 0.75% nPG (w/w) in 5002; group 3, fed 1.5% nPG (w/w) in 5002; group 4 fed 1% (w/w) vitamin E in 5002; and group 5, fed 2% (w/w) vitamin E also in 5002. Mice were fed for 23 days. On day 23 mice were exposed to 32 mg m-3 (8 ppm) phosgene for 20 min (640 mg. min m-3) in a whole-body exposure chamber. Survival rates were determined at 12 and 24 h. In mice that died within 12 h, the lungs were removed and lung wet weights, dry weights, wet/dry weight ratios, lipid peroxidation (thiobarbituric acid reactive substances, TBARS) and glutathione (GSH) were assessed. Vitamin E had no positive effect on any outcome measured. There was no significant difference between 1.5% nPG and any parameter measured or survival rate compared with 5002 + phosgene. However, dietary treatment with 0.75% nPG significantly increased survival rate (P </= 0.002) and lowered TBARS (P </= 0.05) compared with 5002 + phosgene at 12 h after exposure. Mice fed 0.75% nPG had a lower wet/dry wt ratio compared with those fed 1.5% nPG and a significantly increased lung tissue GSH 36%, compared with the 5002 + phosgene group. In conclusion, dietary treatment with a low level of the antioxidant nPG protected mice by decreasing lipid peroxidation and increasing lung tissue GSH. The higher level of nPG and both levels of vitamin E diets were ineffective, suggesting that a ceiling threshold level of antioxidants in lung tissue is required for survival against phosgene-induced lung injury. Published in 2001 by John Wiley & Sons, Ltd.

In vitro adduct formation of phosgene with albumin and hemoglobin in human blood

The development of procedures for retrospective detection and quantitation of exposure to phosgene, based on adducts to hemoglobin and albumin, is described. Upon incubation of human blood with [(14)C]phosgene (0-750 microM), a significant part of radioactivity (0-13%) became associated with globin and albumin. Upon Pronase digestion of globin, one of the adducts was identified as the pentapeptide O=C-(V-L)-S-P-A, representing amino acid residues 1-5 of alpha-globin, with a hydantoin function between N-terminal valine and leucine. Micro-LC/tandem MS analyses of tryptic as well as V8 protease digests identified one of the adducts to albumin as a urea resulting from intramolecular bridging of lysine residues 195 and 199. The adducted tryptic fragment could be sensitively analyzed by means of micro-LC/tandem MS with multiple-reaction monitoring (MRM), enabling the detection in human blood of an in vitro exposure level of >/=1 microM phosgene.

beta-adrenergic stimulation restores rat lung ability to clear edema in ventilator-associated lung injury

Mechanical ventilation with high tidal volume (HVT) causes lung injury and decreases the lung's ability to clear edema in rats. beta-adrenergic agonists increase active Na(+) transport and lung edema clearance in normal rat lungs by stimulating apical Na(+) channels and basolateral Na,K-ATPase in alveolar epithelial cells. We studied whether beta-adrenergic agonists could restore lung edema clearance in rats ventilated with HVT (40 ml/kg, peak airway pressure of 35 cm H(2)O) for 40 min. The ability of rat lungs to clear edema decreased by approximately 50% after 40 min of HVT ventilation. Terbutaline (TERB) and isoproterenol (ISO) increased lung edema clearance in control nonventilated rats (from 0.50 +/- 0. 02 ml/h to 0.81 +/- 0.04 ml/h and 0.99 +/- 0.05 ml/h, respectively) and restored the lung's ability to clear edema in HVT ventilated rats (from 0.25 +/- 0.03 ml/h to 0.64 +/- 0.02 ml/h and 0.88 +/- 0. 09 ml/h, respectively). Disruption of cell microtubular transport system by colchicine inhibited the stimulatory effects of ISO in HVT ventilated rats, whereas beta-lumicolchicine did not affect beta-adrenergic stimulation. The Na,K-ATPase alpha(1)- and beta(1)-subunit mRNA steady state levels were not affected by incubation with ISO for 60 min in alveolar type II cells isolated from control and HVT ventilated rats. The data suggest that beta-adrenergic agonists increased alveolar fluid reabsorption in rats ventilated with HVT by promoting recruitment of ion-transporting proteins from intracellular pools to the plasma membrane of alveolar epithelial cells.

Is the use of catecholamine before ischemic arrest safe? Effect of catecholamine on rat heart ischemia/reperfusion injury

Using an isolated working heart model, we studied the effects of dopamine, adrenaline, or noradrenaline pretreatment on ischemia/reperfusion injury. Hearts from Wistar rats were perfused in the first 20-minute working mode, 15 minutes in Langendorff mode, and in the second 20-minute working mode. Hearts were treated with dopamine (0.52 and 2.60 mmol/L), adrenaline (16 and 80 nmol/L), or noradrenaline (16 and 80 nmol/L) during the second working perfusion, then arrested with St. Thomas' Hospital cardioplegic solution and subjected to global ischemia (37 degrees C or 20 degrees C). During reperfusion, recoveries of cardiac function and creatine kinase leakage were measured. At 37 degrees C, dopamine and adrenaline had a harmful effect at both doses; noradrenaline was harmful at a high dose but beneficial at a low dose. At 20 degrees C, adrenaline, dopamine, and noradrenaline had a harmful effect at high doses but no harmful effect at low doses. To determine the role of beta adrenergic stimulation before ischemia, a dose-response study was undertaken with isoprotelenol and milrinone at 37 degrees C. Combined pretreatment with isoprotelenol and milrinone accelerated ischemia/reperfusion injury dose-dependently. Preischemic beta adrenergic stimulation thus plays a significant role in the deleterious effect of catecholamine pretreatment at high doses. At low doses, however, the effect of the inotropic agent could be changed depending on ischemic temperature. Our results suggest that catecholamine should not be given at high doses before ischemia, regardless of temperature during ischemia.

Signal transduction and regulation of lung endothelial cell permeability. Interaction between calcium and cAMP

Pulmonary endothelium forms a semiselective barrier that regulates fluid balance and leukocyte trafficking. During the course of lung inflammation, neurohumoral mediators and oxidants act on endothelial cells to induce intercellular gaps permissive for transudation of proteinaceous fluid from blood into the interstitium. Intracellular signals activated by neurohumoral mediators and oxidants that evoke intercellular gap formation are incompletely understood. Cytosolic Ca2+ concentration ([Ca2+]i) and cAMP are two signals that importantly dictate cell-cell apposition. Although increased [Ca2+]i promotes disruption of the macrovascular endothelial cell barrier, increased cAMP enhances endothelial barrier function. Furthermore, during the course of inflammation, elevated endothelial cell [Ca2+]i decreases cAMP to facilitate intercellular gap formation. Given the significance of both [Ca2+]i and cAMP in mediating cell-cell apposition, this review addresses potential sites of cross talk between these two intracellular signaling pathways. Emerging data also indicate that endothelial cells derived from different vascular sites within the pulmonary circulation exhibit distinct sensitivities to permeability-inducing stimuli; that is, elevated [Ca2+]i promotes macrovascular but not microvascular barrier disruption. Thus this review also considers the roles of [Ca2+]i and cAMP in mediating site-specific alterations in endothelial permeability.

Effect of preischemic catecholamine treatment on ischemia-reperfusion injury of the myocardium: subtype, dose, and temperature dependency

Preischemic adrenergic stimulation may affect postischemic cardiac function. Using an isolated working heart model, we investigated the effects of preischemic catecholamine treatment on postischemic recovery. Hearts from Wistar rats were perfused in working mode for 20 min, in Langendorff mode for 15 min, and again in working mode for 20 min (W2). Hearts were treated with isoproterenol (8.0 and 40.0 nmol/L), phenylephrine (0.06, 0.30, and 1.50 micromol/L), or epinephrine (16 and 80 nmol/L) during the W2 period and then arrested with St Thomas' Hospital cardioplegic solution (STH) and subjected to global ischemia (37 degrees C or 20 degrees C), followed by reperfusion. At 37 degrees C, isoproterenol had a beneficial effect at the lower dose but a harmful effect at the higher dose; phenylephrine and epinephrine had a harmful effect at all doses. At 20 degrees C, isoproterenol and epinephrine had a harmful effect at a high dose; phenylephrine had no harmful effect at any dose. In a separate study, the influence of calcium modulators (diltiazem and ryanodine, added in the STH) on the catecholamine effect was investigated. The harmful effect of preischemic treatment with isoproterenol (24.0 nmol/L) or phenylephrine (0.9 micromol/L) was abolished by the calcium modulators. Thus, preischemic beta-adrenergic or alpha + beta-adrenergic stimulation has a deleterious effect on postischemic recovery of the myocardium. The effect could be altered depending on the subtype and dose of catecholamine and the ischemic temperature. Intracellular calcium movement could be involved in the mechanism responsible for the harmful effect of preischemic catecholamine treatment.

Posttreatment with eicosatetraynoic acid decreases lung edema in guinea pigs exposed to phosgene: the role of leukotrienes

Acetylenic acids such as 5,8,11,14-eicosatetraynoic acid (ETYA), have been shown to be effective in preventing pulmonary edema formation (PEF). In phosgene-exposed guinea pigs, we examined the effects of ETYA on PEF, measured as real time lung weight gain (lwg). Pulmonary artery pressure (Ppa), airway pressure (Paw), perfusate leukotrienes (LT) C4/D4/E4/B4, and lung tissue lipid peroxidation (TBARS) were measured using the isolated, buffer-perfused lung model. Guinea pigs were challenged to 175 mg/m3 (44 ppm) phosgene for 10 minutes giving a concentration x time product of 1750 mg.min/m3 (437 ppm.min). Five minutes after removal from the exposure chamber, guinea pigs were treated, i.p., with 200 microL of 100 microM ETYA. 200 microL of 50 microM ETYA was added to the perfusate every 40 minutes, beginning at 60 minutes after start of exposure (t = 0). There were four groups in this study: air-treated, phosgene-exposed, ETYA-posttreated + phosgene, and ETYA-posttreated + air ETYA-posttreated + phosgene guinea pigs had significantly lower Ppa (P = .006), Paw (P = .009), and lwg (P = .016) compared with phosgene-exposed animals. Phosgene exposure reduced LTB4 compared with air-treated controls (P = .09). ETYA-posttreatment + phosgene had significantly increased perfusate LTB4 (P = .0006) compared with phosgene exposure only group. Total perfusate, LTC4 + LTD4 + LTE4, was not different between phosgene-exposed, air-treated or ETYA-posttreatment + phosgene over time. Posttreatment with ETYA significantly lowered TBARS formation, 206 +/- 13 versus 285 +/- 23 nmol/mg protein (P = .016), compared with phosgene-exposed lungs. Paradoxically, ETYA posttreatment decreased PEF and lipid peroxidation, but increased sulfidopeptide LT release from the lung during perfusion. We conclude that LTC4/D4/E4, and B4, may play different roles than previously thought for PEF in the isolated perfused lung model.

Dibutyryl cyclic adenosine monophosphate attenuates lung injury caused by cold preservation and ischemia-reperfusion

OBJECTIVE

Dibutyryl adenosine 3',5'cyclic monophosphate (db-cAMP) is a membrane-permeable analog of adenosine 3',5'cyclic monophosphate (cAMP). We examined the effect of db-cAMP against lung injury caused by cold preservation and ischemia-reperfusion.

METHODS

Rats were divided into three groups (each n = 6) according to the presence or absence of db-cAMP in the preservative solution and cold ischemia (4 degrees C for 15 hours). In the fresh group, the lung was flushed with the preservative solution and reperfusion was performed immediately. In the control group and the db-cAMP group, the lung was flushed either with the solution or with a combination of the solution plus db-cAMP, respectively, and preserved at 4 degrees C for 15 hours. The lung was reperfused for 60 minutes in an ex vivo rat lung perfusion model.

RESULTS

The shunt ratios of the reperfused lung in the db-cAMP group were 4.0% +/- 1.6% and 3.4% +/- 1.2% 10 and 60 minutes, respectively, after the initiation of reperfusion, being as low as those in the fresh group and significantly lower than those in the control group (p < 0.01). The wet/dry weight ratio of the lung tissue after reperfusion was 5.99 +/- 1.50 in the db-cAMP group, which was similar to that in the fresh group (5.45 +/- 0.23) and significantly lower than that in the control group (14.20 +/- 3.43) (p < 0.01). Electron microscopic examination showed less damage in the pulmonary arterial endothelium in the db-cAMP group.

CONCLUSIONS

We conclude that db-cAMP attenuates the lung injury by cold preservation and ischemia-reperfusion, at least partly by protection of the vascular endothelium.

Postexposure treatment with aminophylline protects against phosgene-induced acute lung injury

Pretreatment with aminophylline has been shown to protect against various types of acute lung injury. Mechanisms responsible for protection are multifactorial but are thought to involve upregulation of cAMP. While previous studies focused on pretreatment, the present investigation examined post-treatment in rabbits following exposure to a lethal dose of the oxidant gas phosgene. Rabbits, 2-3 kg, were exposed to a cumulative dose of phosgene to attain a c x t exposure effect of 1500 ppm.min. Lungs were isolated in situ and perfused for 90-100 min after exposure with Krebs-Henseleit buffer at 40 mL/min. Pulmonary artery pressure (Ppa), tracheal pressure (Pt), and lung weight gain (lwg) were measured continuously. Leukotrienes C4/D4/E4 were measured in the perfusate every 20 min during perfusion. At the immediate conclusion of the experiment, lung tissue was frozen in liquid N2 and analyzed for reduced GSH, GSSG, cAMP, and lipid peroxidation (TBARS). Post-treatment with aminophylline 80-90 min after exposure significantly lowered Ppa, Pt, and lwg. Aminophylline significantly reduced TBARS and perfusate LTC4/D4/E4, and prevented phosgene-induced decreases in lung tissue cAMP. These data suggest that protective mechanisms observed with aminophylline involve decreased LTC4/D4/E4-mediated pulmonary capillary permeability and attenuated lipid peroxidation. Direct antipermeability effects of cAMP on cellular contraction may also be important in protection against phosgene-induced lung injury.

Pulmonary edema induced by phorbol myristate acetate is attenuated by compounds that increase intracellular cAMP

We have investigated the effect of terbutaline, aminophylline and dibutyryl cyclic AMP (DBcAMP) on phorbol myristate acetate (PMA)-induced acute lung injury in isolated, blood-perfused rabbit lungs. Pulmonary arterial pressure and lung weight were measured for 30 min after a bolus injection of PMA (10 mu g/kg). In the group exposed to PMA alone, the mean pulmonary arterial pressure (PAP) increased from 16.33 + or - 1.28 to 77.30 + or - 6.40 mmHg (P <0.001), and lung weight increased by 70.69 + or - 10.94 g during the 30 min after PMA challenge (P<0.001). Pretreatment with terbutaline, aminophylline or DBcAMP prevented the increases in both PAP and lung weight (P <0.001). Each of the three drugs also prevented the increase in pulmonary vascular permeability induced by PMA: terbutaline, aminophylline, and DBcAMP all significantly reduced the pulmonary capillary filtration coefficient (KfC) as well as the albumin concentration in the lung lavage fluid after PMA exposure. Post-treatment with terbutaline 5 min after PMA administration also had a protective effect. The mechanisms responsible for these protectivp3 effects may all involve an increase in intracellular cAMP, since all three drugs increase cAMP in the lung (though by different mechanisms). Our data further indicate that the inhibition of tumor necrosis factor production may likewise play an important role in the protective effect exerted by these drugs.

Acute lung injury after phosgene inhalation

Phosgene (COCl2) is a colorless oxidant gas which is heavier than air and the lethal exposure dose (LC50) in humans is 500 ppm/min. This gas was originally manufactured as an agent for chemical warfare during World War I and there had been a great deal of studies on phosgene poisoning during the early years of industrial use. It is still widely used in the synthesis of chemicals and plastics. In the modern era, however, phosgene poisoning is relatively uncommon except in accidental exposures. In Korea, there has been no report about lung injury from phosgene inhalation. We present a clinical experience with six patients accidentally exposed to phosgene.

Role of the lung in accumulation and metabolism of xenobiotic compounds--implications for chemically induced toxicity

The mammalian lung is exposed to and affected by many airborne and bloodborne foreign compounds. This review summarizes the role of lung in accumulation and metabolism of xenobiotics, some of which are spontaneously reactive or are metabolically activated to toxic intermediates. The specific architectural arrangement of mammalian lung favors that so-called pneumophilic drugs are filtered out of the blood and are retained within the tissue as shown in particular for amphetamine, chlorphentermine, amiodarone, imipramine, chlorpromazine, propranolol, local anaesthetics, and some miscellaneous therapeutics. There is strong evidence that intrapulmonary distribution activity and regulation of drug-metabolizing enzymes in lung is distinct from liver. This review focuses on the metabolic rate of selected compounds in lung such as 5-fluoro-2'-deoxyuridine, local anesthetics, nicotine, benzo(alpha)pyrene, ipomeanol, 4-methylnitrosamino-1-(3-pyridyl)-1-butanone. It is widely accepted that the formation of radical species is a key event in the pneumotoxic mechanisms induced by bleomycin, paraquat, 3-methylindole, butylhydroxytoluene, or nitrofurantoin. Finally, methodological approaches to assess the capacity of lung to eliminate foreign compounds as well as biochemical features of the pulmonary tissue are evaluated briefly.

Phosgene effects on F-actin organization and concentration in cells cultured from sheep and rat lung

Pulmonary edema and immunosuppression of the lung are primary causes of debilitation and death from phosgene gas exposure. The pathophysiology that gives rise to these conditions shares a common clinical pathway. However, the target cells and lesions that disrupt normal barrier function and immune response of the lung are complex and poorly understood. Using confocal laser microscopy and FITC-conjugated phalloidin, we have studied the effects of phosgene on F-actin in endothelial cells from sheep pulmonary arteries and epithelial cells from rat tracheal explants. Image analyses from attached culture systems indicate that F-actin was a sensitive target molecule in both species. Exposures ranging from 0.15 to 1.0 x LCt50 for sheep in vivo (3300 ppm.min) produced immediate, dose-dependent decreases in average F-actin content of cultured endothelial cells. Dense peripheral bands and stress fibers were diminished and partially disrupted but were not destroyed by these doses. Changes in ultrastructure and the permeability barrier of endothelial tissues included separation of basal lamina and development of paracellular leakage paths. Phosgene also decreased the F-actin in airway epithelial cells and potentiated phenotypic transformations that gave rise to progeny with dendritic processes. Differences in endothelial and airway epithelial response indicate that the cytoskeletal effects of phosgene were cell-type specific. Disruption of basal lamina, depletion of F-actin, and development of endothelial leakage paths may contribute to decreased barrier function and increased permeability of vascular tissues. Phosgene-induced transformations that involved F-actin reorganization and appearance of dendritic cells among airway epithelial may affect other functions of the lung.

Adenosine protects ultrastructure of isolated rat lungs against fat emulsion injury

In isolated rat lungs subjected to fat emulsion damage, a model simulating adult respiratory distress syndrome, we have previously reported that adenosine (ADO) reduces pulmonary vascular resistance (PVR) and the fluid filtration rate (FFR). In the present study the aim was to examine morphologically this effect of ADO. Two groups of isolated rat lungs were subjected to the injury. Marked and significant differences were found between the groups; in lungs not given ADO, FFR and airway pressure were higher and, as evaluated by electron microscopy, the endothelial lining was thin and partly disrupted. The epithelial cells of the alveolar walls were also partly disrupted and the alveolar septa were split enclosing interstitial edema. In lungs receiving ADO from the onset of exposure to fat emulsion, FFR was lower and ultrastructure did not differ from non-injured non-treated controls perfused for the same length of time.

Mechanisms underlying enhanced responses of J receptors of cats to excitants in pulmonary oedema

1. The responses of J receptors to certain excitants were recorded during pulmonary oedema produced by phosgene gas (320-1080 p.p.m.) or alloxan, 150 mg kg-1 i.v., in cats anaesthetized with sodium pentobarbitone, 35 mg kg-1 I.P. 2. The responses of fourteen (out of fifteen) J receptors to phenyl diguanide (PDG) were greatly enhanced after phosgene, the enhancement being highly significant (P = < 0.01) in twenty-one out of twenty-six responses. The enhancements were also highly significant after alloxan in the case of another twelve receptors. Similar enhancements were observed in the case of responses to nicotine and capsaicin. This suggests that the enhancement of the responses of J receptors to excitants occurs in a non-specific manner after phosgene and alloxan. 3. The enhanced responses occurred in the absence of any significant increase in the estimated concentration of the excitants in pulmonary artery blood. 4. The enhanced responses to PDG were not closely related to the oedema-induced activity; several occurred during periods of silence of the receptors and in thirteen receptors the enhanced responses occurred before the increase in the oedema-induced activity had begun. 5. A possible role of histamine, 5-HT, prostaglandins and bradykinin in enhancing the responses to PDG after phosgene was excluded. 6. The results therefore suggest that the non-specific enhancement of the responses of the J receptors to excitants must be due to the increased permeability of the capillaries produced by phosgene and alloxan leading to greater movement of the excitants to the J receptors. However, certain unidentified factors may also be involved.

Role of phosphodiesterases in the regulation of endothelial permeability in vitro

Neutrophil-derived hydrogen peroxide (H2O2) is believed to play an important role in the pathogenesis of vascular injury and pulmonary edema. H2O2 time- and dose-dependently increased the hydraulic conductivity and decreased the selectivity of an endothelial cell monolayer derived from porcine pulmonary arteries. Effects of H2O2 on endothelial permeability were completely inhibited by adenylate cyclase activation with 10(-12) M cholera toxin or 0.1 microM forskolin. 10(-8) M Sp-cAMPS, a cAMP-dependent protein kinase A agonist, was similarly effective. The phosphodiesterase (PDE) inhibitors motapizone (10(-4) M), rolipram (10(-6) M), and zardaverine (10(-8) M), which specifically inhibit PDE-isoenzymes III, IV, and III/IV potently blocked H2O2-induced endothelial permeability when combined with 10(-6) M prostaglandin E1. Overall cellular cAMP content and inhibition of H2O2 effects on endothelial permeability were poorly correlated. H2O2 exposure resulted in a rapid and substantial decrease in endothelial cAMP content. The analysis of the PDE isoenzyme spectrum showed high activities of isoenzymes II, III, and IV in porcine pulmonary endothelial cells. The data suggest that adenylate cyclase activation/PDE inhibition is a powerful approach to block H2O2-induced increase in endothelial permeability. This concept appears especially valuable when endothelial PDE isoenzyme pattern and PDE inhibitor profile are matched optimally.

Adenosine modulates vascular resistance and fluid filtration in isolated rat lungs

In adult respiratory distress syndrome, a major concern is to reduce increments in pulmonary vascular resistance (PVR) and maintain the patency of lung microvessels. We have investigated the effects of adenosine, a potent systemic vasodilator, on PVR and fluid filtration rate (FFR) in isolated blood-perfused rat lungs. The preparations were undamaged or subjected to fat emulsion-induced injury simulating ARDS. In undamaged lungs adenosine caused a significant dose-dependent reduction of hypoxia-induced increases in PVR. Furthermore, the increase in FFR upon elevation of left atrial pressure by 0.77 kPa was significantly hampered by adenosine, 24 nmol.ml-1.min-1. Employing the same rate of infusion, adenosine, in a group of injured preparations, significantly reduced the rise in PVR towards baseline and completely abolished the further increase upon a superimposed injection of serotonin. In another series of preparations with lung injury randomly assigned to an adenosine group and a control group, adenosine significantly reduced FFR. Thus, adenosine, even when infused at low rates, reduced increments in PVR and fluid filtration, both in undamaged and in fat emulsion-injured isolated lungs.

Norepinephrine and iloprost improve barrier function of human endothelial cell monolayers: role of cAMP

The barrier function of human artery endothelial cells was improved by addition of agents that increase the cellular adenosine 3',5'-cyclic monophosphate (cAMP) concentration. Together with a decrease in the passage rate of peroxidase, an increase in the transendothelial electrical resistance was observed. A direct correlation was found between the relative increases in cellular cAMP concentration and the relative decrease in peroxidase passage after incubation of the cells with forskolin (0.25 and 2.5 microM), the beta-adrenergic agonist isoproterenol (10 microM), and the stable prostacyclin analogue iloprost (10 microM). Norepinephrine (10 microM) reduced the peroxidase passage to a much larger extent (40% reduction) than might be expected on the basis of a small increase of cAMP concentration. This small increase in cAMP (44%) was the result of interactions of norepinephrine with beta-adrenergic receptors, which increase cAMP, and alpha-adrenergic receptors, which decrease cAMP. The relatively strong reduction in permeability (also found in the presence of the alpha-adrenergic antagonist phentolamine) suggests that an additional cAMP-independent mechanism underlaid the barrier-improving effect of norepinephrine. A marked elevation of cAMP by forskolin was accompanied by a disappearance of F-actin and myosin from stress fibers. They were found diffusely spread over the cell, and F-actin in the cell periphery became prominently visible.

Attenuation of LPS-induced neutrophil thromboxane b2 release and chemiluminescence

Polymorphonuclear leukocytes (PMN) may play a key role in acute lung injury and ARDS. The mechanisms of PMN-mediated lung injury include the release of inflammatory mediators, such as oxygen free radicals which cause direct tissue injury, and arachidonic acid metabolites which cause pulmonary vasoconstriction and increased vascular permeability. The goals of this in vitro study were 1) to assess the effects of PMN-activating agents (lipopolysaccharide, LPS; phorbol myristate acetate, PMA; tumor necrosis factor, TNF) on PMN thromboxane B2 (TXB2) release and oxygen free radical production and 2) to determine the effects of agents purported to suppress PMN activity (pentoxifylline, PTX; adenosine; dibutyryl cyclic AMP, DBcAMP; and terbutaline, TBN) on activator-induced PMN TXB2 release and oxygen free radical production. PMN TXB2 release was determined by radioimmunoassay and oxygen free radical production was monitored by chemiluminescence. Our results show that 1) LPS and PMA significantly increase PMN TXB2 release, whereas tumor necrosis factor (TNF) has no effect; 2) LPS and PMA significantly increase PMN chemiluminescence; 3) DBcAMP and TBN significantly reduce LPS-induced PMN TXB2 release whereas PTX and adenosine do not; 4) TBN significantly reduces PMA-induced PMN TXB2 release whereas other agents do not; 5) All agents (PTX, adenosine, DBcAMP, and TBN) significantly reduce LPS-induced PMN chemiluminescence but none attenuate PMA-induced PMN chemiluminescence. We conclude that: LPS and PMA activate PMN manifested by TXB2 release and chemiluminescence. Additionally, all the PMN suppressing agents do attenuate some PMN functions. Of interest, PTX, adenosine, DBcAMP, and TBN have different effects depending upon functional assay and activating agent. It will be important to investigate the mechanisms by which PMN suppressing agents alter signal transduction resulting in differential effects on PMN function.

Ibuprofen prevents oxidant lung injury and in vitro lipid peroxidation by chelating iron

Because ibuprofen protects from septic lung injury, we studied the effect of ibuprofen in oxidant lung injury from phosgene. Lungs from rabbits exposed to 2,000 ppm-min phosgene were perfused with Krebs-Henseleit buffer at 50 ml/min for 60 min. Phosgene caused no increase in lung generation of cyclooxygenase metabolites and no elevation in pulmonary arterial pressure, but markedly increased transvascular fluid flux (delta W = 31 +/- 5 phosgene vs. 8 +/- 1 g unexposed, P less than 0.001), permeability to albumin (125I-HSA) lung leak index 0.274 +/- 0.035 phosgene vs. 0.019 +/- 0.001 unexposed, P less than 0.01; 125I-HSA lavage leak index 0.352 +/- 0.073 phosgene vs. 0.008 +/- 0.001 unexposed, P less than 0.01), and lung malondialdehyde (50 +/- 7 phosgene vs. 24 +/- 0.7 mumol/g dry lung unexposed, P less than 0.01). Ibuprofen protected lungs from phosgene (delta W = 10 +/- 2 g; lung leak index 0.095 +/- 0.013; lavage leak index 0.052 +/- 0.013; and malondialdehyde 16 +/- 3 mumol/g dry lung, P less than 0.01). Because iron-treated ibuprofen failed to protect, we studied the effect of ibuprofen in several iron-mediated reactions in vitro. Ibuprofen attenuated generation of .OH by a Fenton reaction and peroxidation of arachidonic acid by FeCl3 and ascorbate. Ibuprofen also formed iron chelates that lack the free coordination site required for iron to be reactive. Thus, ibuprofen may prevent iron-mediated generation of oxidants or iron-mediated lipid peroxidation after phosgene exposure. This suggests a new mechanism for ibuprofen's action.

Attenuation of tumor necrosis factor-induced endothelial cell cytotoxicity and neutrophil chemiluminescence

Our laboratory has previously shown that the administration of tumor necrosis factor (TNF), a cytokine produced by activated mononuclear cells, to guinea pigs produces a syndrome similar to gram-negative sepsis or ARDS. Pentoxifylline (PTX), a methylxanthine, protects against TNF-induced and sepsis-induced acute lung injury in vivo. We now report on in vitro cellular studies of PMN-mediated cellular injury and its attenuation. We studied TNF-induced bovine pulmonary artery endothelial cell (EC) cytotoxicity both with and without PMN. A 51Cr release assay was used to measure EC damage. Further, we investigated PMN function in response to TNF by measuring chemiluminescence. Agents that attenuate EC damage and PMN activation were evaluated in the above assays. Results revealed that TNF causes EC injury (p less than 0.05) and PMN increase TNF-induced EC injury. Furthermore, PTX, aminophylline (AMPH), caffeine, and forskolin attenuate TNF-induced EC cytotoxicity only in the presence of PMN (p less than 0.05). Of interest, dibutyryl cAMP (DBcAMP) protects EC from TNF-induced injury both with and without PMN. Agents that may increase cAMP levels in PMN (PTX, DBcAMP, forskolin, isobutyl methylxanthine, and terbutaline) significantly attenuate TNF-induced PMN chemiluminescence (p less than 0.05). We conclude that TNF causes EC damage and PMN increase this damage. Furthermore, PTX, AMPH, caffeine, and forskolin can attenuate TNF-induced EC injury in the presence of PMN, whereas DBcAMP attenuates TNF-induced EC injury with and without PMN. In addition, agents that may increase intracellular cAMP levels in PMN can attenuate TNF-induced PMN chemiluminescence. Thus, these agents likely attenuate TNF-induced PMN-mediated EC injury through their inhibitory effects on PMN.