Phosgene inhalation toxicity: Update on mechanisms and mechanism-based treatment strategies.

Phosgene (carbonyl dichloride) gas is an indispensable high-production-volume chemical intermediate used worldwide in numerous industrial processes. Published evidence of human exposures due to accidents and warfare (World War I) has been reported; however, these reports often lack specificity because of the uncharacterized exposure intensities of phosgene and/or related irritants. These may include liquid or solid congeners of phosgene, including di- and triphosgene and/or the respiratory tract irritant chlorine which are often collectively reported under the umbrella of phosgene exposure without any appreciation of their differences in causing acute lung injury (ALI). Among these irritants, phosgene gas is somewhat unique because of its poor water solubility. This prevents any appreciable retention of the gas in the upper airways and related trigeminal sensations of irritation. By contrast, in the pulmonary compartment, amphiphilic surfactant might scavenge this lipophilic gas. The interaction of phosgene and the surfactant may affect basic physiological functions controlled by Starling's and Laplace's laws, which can be followed by cardiogenic pulmonary edema. The phenotypic manifestations are dependent on the concentration × exposure duration (C × t); the higher the C × t is, the less time that is required for edema to appear. It is hypothesized that this type of edema is caused by cardiovascular and colloid osmotic imbalances to initial neurogenic events but not because of the injury itself. Thus, hemodynamic etiologies appear to cause imbalances in extravasated fluids and solute accumulation in the pulmonary interstitium, which is not drained away by the lymphatic channels of the lung. The most salient associated findings are hemoconcentration and hypoproteinemia. The involved intertwined pathophysiological processes coordinating pulmonary ventilation and cardiopulmonary perfusion under such conditions are complex. Pulmonary arterial catheter measurements on phosgene-exposed dogs provided evidence of 'cor pulmonale', a form of acute right heart failure produced by a sudden increase in resistance to blood flow in the pulmonary circulation about 20 h postexposure. The objective of this review is to critically analyze evidence from experimental inhalation studies in rats and dogs, and evidence from accidental human exposures to better understand the primary and secondary events causing cardiopulmonary dysfunction and an ensuing life-threatening lung edema. Mechanism-based diagnostic and therapeutic approaches are also considered for this form of cardiogenic edema.

Phosgene inhalation causes hemolysis and acute lung injury.

Phosgene (Carbonyl Chloride, COCl2) remains an important chemical intermediate in many industrial processes such as combustion of chlorinated hydrocarbons and synthesis of solvents (degreasers, cleaners). It is a sweet smelling gas, and therefore does not prompt escape by the victim upon exposure. Supplemental oxygen and ventilation are the only available management strategies. This study was aimed to delineate the pathogenesis and identify novel biomarkers of acute lung injury post exposure to COCl2 gas. Adult male and female C57BL/6 mice (20-25 g), exposed to COCl2 gas (10 or 20 ppm) for 10 min in environmental chambers, had a dose dependent reduction in PaO2 and an increase in PaCO2, 1 day post exposure. However, mortality increased only in mice exposed to 20 ppm of COCl2 for 10 min. Correspondingly, these mice (20 ppm) also had severe acute lung injury as indicated by an increase in lung wet to dry weight ratio, extravasation of plasma proteins and neutrophils into the bronchoalveolar lavage fluid, and an increase in total lung resistance. The increase in acute lung injury parameters in COCl2 (20 ppm, 10 min) exposed mice correlated with simultaneous increase in oxidation of red blood cells (RBC) membrane, RBC fragility, and plasma levels of cell-free heme. In addition, these mice had decreased plasmalogen levels (plasmenylethanolamine) and elevated levels of their breakdown product, polyunsaturated lysophosphatidylethanolamine, in the circulation suggesting damage to cellular plasma membranes. This study highlights the importance of free heme in the pathogenesis of COCl2 lung injury and identifies plasma membrane breakdown product as potential biomarkers of COCl2 toxicity.

Characterization of a nose-only inhaled phosgene acute lung injury mouse model.

CONTEXT: Phosgene's primary mode of action is as a pulmonary irritant characterized by its early latent phase where life-threatening, non-cardiogenic pulmonary edema is typically observed 6-24 h post-exposure. OBJECTIVE: To develop an inhaled phosgene acute lung injury (ALI) model in C57BL/6 mice that can be used to screen potential medical countermeasures. METHODS: A Cannon style nose-only inhalation exposure tower was used to expose mice to phosgene (8 ppm) or air (sham). An inhalation lethality study was conducted to determine the 8 ppm median lethal exposure (LCt50) at 24 and 48 h post-exposure. The model was then developed at 1.2 times the 24 h LCt50. At predetermined serial sacrifice time points, survivors were euthanized, body and lung weights collected, and lung tissues processed for histopathology. Additionally, post-exposure clinical observations were used to assess quality of life. RESULTS AND DISCUSSION: The 24-hour LCt50 was 226 ppm*min (8 ppm for 28.2 min) and the 48-hour LCt50 was 215 ppm*min (8 ppm for 26.9 min). The phosgene exposed animals had a distinct progression of clinical signs, histopathological changes and increased lung/body weight ratios. Early indicators of a 1.2 times the 24-hour LCt50 phosgene exposure were significant changes in the lung-to-body weight ratios by 4 h post-exposure. The progression of clinical signs and histopathological changes were important endpoints for characterizing phosgene-induced ALI for future countermeasure studies. CONCLUSION: An 8 ppm phosgene exposure for 34 min (1.2 × LCt50) is the minimum challenge recommended for evaluating therapeutic interventions. The predicted higher mortality in the phosgene-only controls will help demonstrate efficacy of candidate treatments and increase the probability that a change in survival rate is statistically significant.

Acute nose-only inhalation exposure of rats to di- and triphosgene relative to phosgene.

Groups of young adult Wistar rats were acutely exposed to trichloromethyl chloroformate (diphosgene) and bis(trichloromethyl) carbonate (triphosgene) vapor atmospheres using a directed-flow nose-only mode of exposure. The exposure duration used was 240 min. The median lethal concentration (LC50) of diphosgene and triphosgene was 13.9 and 41.5 mg/m3, respectively. Based on the molar exposure concentrations, the LC50s of phosgene (previously published), diphosgene, and triphosgene were 0.07, 0.07, and 0.14 mmol/m3, respectively. Although the principal toxic mode of action of the volatile diphosgene was similar to phosgene gas, the vapor phase of triphosgene appeared to be different to that of phosgene and diphosgene based on a more persistent occurrence of signs of respiratory distress and a biphasic onset of mortality. While all substances caused mortality within 1 day postexposure, triphosgene induced a second phase of mortality 11?14 days postexposure. The vapor saturation concentration of triphosgene at ambient temperature is ?100 times its LC50. In summary, triphosgene-induced lung injury patterns are different from that of phosgene and diphosgene. More research is needed to close the substantial data gaps of triphosgene.

Pentoxifylline inhibits intercellular adhesion molecule-1 (ICAM-1) and lung injury in experimental phosgene-exposure rats.

Phosgene inhalation results in acute lung injury (ALI) mostly, pulmonary edema and even acute respiratory distress syndrome, but there is no specific antidote. Inflammatory cells play an important role in the ALI caused by phosgene. Intercellular adhesion molecule-1 (ICAM-1) is a critical factor for inflammatory organ injury. We hypothesized that pentoxifylline (PTX), an inhibitor of leukocyte activation, would have a protective effect on experimental phosgene-induced lung injury rats by inhibiting ICAM-1. To prove this hypothesis, we used rat models of phosgene (400 ppm x 1 min)-induced injury to investigate: (1) the time course of lung injury (control 1, 3, 6, 12, 24, and 48 h group), including pathological changes in hematoxylin and eosin staining and transmission electron microscope, myeloperoxidase (MPO) activity by colorimetric method and ICAM-1 protein level detected by western blot, (2) At 3 h after phosgene exposure, protective effects of different dosages of PTX (50 mg/kg and 100 mg/kg) administration were evaluated by MPO activity, ICAM-1 differential expression and WBC count in bronchoalveolar lavage fluid. The results showed that inflammatory cells emerged out of lung blood vessels at 3 h after phosgene exposure. The MPO activity of lung tissue increased significantly from 3 to 48 h after phosgene exposure (P < 0.05) and ICAM-1 expression presented a similar change, especially at 3 h and 24 h (P < 0.05). After pretreatment and treatment with PTX (100 mg/kg), significant protective effects were shown (P < 0.05). These data supported our hypothesis that PTX reduced phosgene-induced lung injury, possibly by inhibiting ICAM-1 differential expression.

Genomic analysis of murine pulmonary tissue following carbonyl chloride inhalation.

Carbonyl chloride (phosgene) is a toxic industrial compound widely used in industry for the production of synthetic products, such as polyfoam rubber, plastics, and dyes. Exposure to phosgene results in a latent (1-24 h), potentially life-threatening pulmonary edema and irreversible acute lung injury. A genomic approach was utilized to investigate the molecular mechanism of phosgene-induced lung injury. CD-1 male mice were exposed whole body to either air or a concentration x time amount of 32 mg/m3 (8 ppm) phosgene for 20 min (640 mg x min/m3). Lung tissue was collected from air- or phosgene-exposed mice at 0.5, 1, 4, 8, 12, 24, 48, and 72 h postexposure. RNA was extracted from the lung and used as starting material for the probing of oligonucleotide microarrays to determine changes in gene expression following phosgene exposure. The data were analyzed using principal component analysis to determine the greatest sources of data variability. A three-way analysis of variance based on exposure, time, and sample was performed to identify the genes most significantly changed as a result of phosgene exposure. These genes were rank ordered by p values and categorized based on molecular function and biological process. Some of the most significant changes in gene expression reflect changes in glutathione synthesis and redox regulation of the cell, including upregulation of glutathione S-transferase alpha-2, glutathione peroxidase 2, and glutamate-cysteine ligase, catalytic subunit (also known as gamma-glutamyl cysteine synthetase). This is in agreement with previous observations describing changes in redox enzyme activity after phosgene exposure. We are also investigating other pathways that are responsive to phosgene exposure to identify mechanisms of toxicity and potential therapeutic targets.

Colchicine decreases airway hyperreactivity after phosgene exposure.

Phosgene (COCl(2)) exposure affects an influx of inflammatory cells into the lung, which can be reduced in an animal model by pretreatment with colchicine. Inflammation in the respiratory tract can be associated with an increase in airway hyperreactivity. We tested the hypotheses that (1) phosgene exposure increases airway reactivity and (2) colchicine can decrease this elevation. Sprague Dawley rats (70 d old; male) were exposed to 1 ppm COCl(2) for 1 h. Airway reactivity was tested at 0, 4, and 24 h postexposure by infusing anesthetized animals intravenously with acetylcholine and assessing expiratory resistance and dynamic compliance. Immediately and 4 h postexposure, a significant change in expiratory resistance and dynamic compliance was observed in those animals exposed to COCl(2), while at 24 h this response was greater. A second experiment was performed in rats pretreated with colchicine (1 mg/kg) or saline given intraperitoneally, exposed to 1 ppm COCl(2) for 1 h, with both expiratory resistance and dynamic compliance assessed at 24 h. After exposure, cell differentials and protein in lavage were also quantitated. The results indicate that colchicine decreased neutrophil influx, protein accumulation, and changes in both expiratory resistance and dynamic compliance after COCl(2) exposure. Colchicine may affect injury and changes in expiratory resistance and dynamic compliance by diminishing the incursion of inflammatory cells, but other properties of this medication may also be responsible for the observed results.

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.

Chronological changes in electrolyte levels in arterial blood and bronchoalveolar lavage fluid in mice after exposure to an edemagenic gas.

Detection of acute lung injury is important if therapeutic medical countermeasures are to be used to reduce toxicity in a timely manner. Indicators of injury may aid in the eventual treatment course and enhance the odds of a positive outcome following a toxic exposure. This study was designed to investigate the effects of a toxic exposure to the industrial irritant gas phosgene on the electrolyte levels in arterial blood and bronchoalveolar lavage fluid (BALF). Phosgene is a well-known chemical intermediate capable of producing life-threatening pulmonary edema within hours after exposure. Four groups of 40 Crl:CD-1(ICR)BR male mice were exposed whole-body to either air or phosgene at a concentration x time (c x t) amount of 32-42 mg/m(3) (8-11 ppm) phosgene for 20 min (640-840 mg x min/m(3)). BALF from air- or phosgene-exposed mice was taken at 1, 4, 8, 12, 24, 48, or 72 h postexposure. After euthanasia, the trachea was excised, and 800 microl saline was instilled into the lungs. The lungs were washed 5x. Eighty microliters of BALF was placed in a cartridge and inserted into a clinical i-STAT analyzer. Na(+), Cl(-), K(+), and ionized Ca(2+) were analyzed. Arterial blood electrolyte levels were also analyzed in four additional groups of air- or phosgene-exposed mice. The left lung was removed to determine wet weight (WW), an indicator of pulmonary edema. Na(+) was significantly higher in air than in phosgene-exposed mice at 4, 8, and 12 h postexposure. Temporal changes in BALF Cl(-) in phosgene mice were not statistically different from those in the air mice. Both Ca(2+) and K(+) were significantly higher than in the air-exposed mice over 72 h, p < or = 0.03 and p < or = 0.001 (two-way analysis of variance, ANOVA), respectively. Significant changes in BALF K(+) and Ca(2+) occurred as early as 4 h postexposure in phosgene, p < or = 0.005, versus air-exposed mice. Over time, there were no significant changes in arterial blood levels of Na(+), Cl(-), or Ca(2+) for animals exposed to air versus phosgene. However, arterial K(+) concentrations were significantly higher, p < or = 0.05, than in air-exposed mice across all time points, with the highest K(+) levels of 7 mmol/L occurring at 8 h and 24 h after exposure. Phosgene caused a time-dependent significant increase in WW from 4 to 12 h, p < or = 0.025, compared with air-exposed mice. These data demonstrate that measuring blood K(+) levels 1 h after exposure along with BALF Na(+), K(+), and Ca(2+) may serve as an alternate indicators of lung injury since both K(+) and Ca(2+) follow temporal increases in air-blood barrier permeability as measured by wet weight.

Pathophysiological responses following phosgene exposure in the anaesthetized pig.

This study aimed to develop a reproducible model of phosgene-induced lung injury in the pig to facilitate the future development of therapeutic strategies. Ten female young adult large white pigs were used. Following induction of anaesthesia using a halothane/oxygen/nitrous oxide mixture, arterial and venous catheters were inserted together with a pulmonary artery thermodilution catheter, and a suprapubic urinary catheter by laparotomy. Anaesthesia was maintained throughout the experiment by intravenous infusion of ketamine, midazolam and alfentanil. On completion of surgery the animals were allowed to equilibrate for 1 h and then were divided into two groups. Group 1 (n = 5) was exposed to phosgene for 10 min (mean Ct = 2443 +/- 35 mg min m(-3)) while spontaneously breathing, whereas control animals (Group 2 n = 5) were exposed to air. At 30 min post-exposure, anaesthesia was deepened in order to allow the initiation of intermittent positive pressure ventilation and the animals were monitored for up to 24 h. Cardiovascular and respiratory parameters were monitored every 30 min and blood samples were taken for arterial and mixed venous blood gas analysis and clinical chemistry. A detailed post-mortem and histopathology was carried out on all animals following death or euthanasia at the end of the 24-h monitoring period. Control animals (Group 2) all survived until the end of the 24-h monitoring period with normal pathophysiological parameters. Histopathology showed only minimal passive congestion of the lung. Following exposure to phosgene (Group 1) there was one survivor to 24 h, with the remainder dying between 16.5 and 23 h (mean = 20 h). Histopathology from these animals showed areas of widespread pulmonary oedema, petechial haemorrhage and bronchial epithelial necrosis. There was also a significant increase in lung wet weight/body weight ratio (P < 0.001). During and immediately following exposure, a transient decrease in oxygen saturation and stroke volume index was observed. From 6 h there were significant decreases in arterial pH (P < 0.01), P(a)O(2) (P < 0.01) and lung compliance (P < 0.01), whereas oxygen delivery and consumption was reduced from 15 h onwards in phosgene-exposed animals. Mean pulmonary artery pressure of phosgene-exposed animals was increased from 15 h post-exposure, with periods of increased pulmonary vascular resistance index being recorded from 9 h onwards. We have developed a reproducible model of phosgene-induced lung injury in the anaesthetized pig. We have followed changes in cardiovascular and pulmonary dynamics for up to 24 h after exposure in order to demonstrate evidence of primary acute lung injury from 16 h post-exposure. Histopathology showed evidence of widespread damage to the lung and there was also a significant increase in lung wet weight/body weight ratio (P < 0.001).

Temporal changes in respiratory dynamics in mice exposed to phosgene.

One hallmark of phosgene inhalation toxicity is the latent formation of life-threatening, noncardiogenic pulmonary edema. The purpose of this study was to investigate the effect of phosgene inhalation on respiratory dynamics over 12 h. CD-1 male mice, 25-30 g, were exposed to 32 mg/m(3) (8 ppm) phosgene for 20 min (640 mg min/m(3)) followed by a 5-min air washout. A similar group of mice was exposed to room air for 25 min. After exposure, conscious mice were placed unrestrained in a whole-body plethysmograph to determine breathing frequency (f), inspiration (Ti) and expiration (Te) times, tidal volume (TV), minute ventilation (MV), end inspiratory pause (EIP), end expiratory (EEP) pause, peak inspiratory flows (PIF), peak expiratory flows (PEF), and a measure of bronchoconstriction (Penh). All parameters were evaluated every 15 min for 12 h. Bronchoalveolar lavage fluid (BALF) protein concentration and lung wet/dry weight ratios (W/D) were also determined at 1, 4, 8, and 12 h. A treatment x time repeated-measures two-way analysis of variance (ANOVA) revealed significant differences between air and phosgene for EEP, EIP, PEF, PIF, TV, and MV, p < or =.05, across 12 h. Phosgene-exposed mice had a significantly longer mean Ti, p < or =.05, compared with air-exposed mice over time. Mice exposed to phosgene showed marked increases (approximately double) in Penh across all time points, beginning at 5 h, when compared with air-exposed mice, p < or =.05. BALF protein, an indicator of air/blood barrier integrity, and W/D were significantly higher, 10- to 12-fold, in phosgene-exposed than in air-exposed mice 4-12 h after exposure, p

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

Posttreatment with ETYA protects against phosgene-induced lung injury by amplifying the glutathione to lipid peroxidation ratio.

Exposure to phosgene has been shown to cause severe and life-threatening pulmonary edema. There is evidence that successful treatment of phosgene-induced acute lung injury may be related to increased antioxidant activity. 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. Lipid peroxidation (thiobarbituric acid-reactive substance, TBARS) and total glutathione (GSH) were measured in lung tissue from isolated, buffer-perfused guinea pig lungs at 180 min after start of exposure. Guinea pigs were challenged with 175 mg/m(3) (44 ppm) phosgene for 10 min (1750 mg( small middle dot)min/m(3)). Five minutes after removal from the exposure chamber, guinea pigs were treated, ip, with 200 microl of 100 microM ETYA in ethanol (ETOH). Two hundred microliters of 50 microM ETYA in ETOH was added to the 200 ml perfusate every 40 min beginning at 60 min after start of exposure (t = 0). There were four groups in this study: air-exposed, phosgene-exposed, phosgene + ETYA-posttreated, and air + ETYA-posttreated. Posttreatment with ETYA prevented GSH depletion, 2. 7 +/- 0.5 micromol/mg protein versus 1 +/- 0.2 micromol/mg protein, for the untreated phosgene-exposed lungs (p < or =.05). ETYA posttreatment also significantly decreased PEF (p

Efficacy of ibuprofen and pentoxifylline in the treatment of phosgene-induced acute lung injury.

Phosgene, a highly reactive former warfare gas, is a deep lung irritant which produces adult respiratory distress syndrome (ARDS)-like symptoms following inhalation. Death caused by phosgene involves a latent, 6-24-h, fulminating non-cardiogenic pulmonary edema. The following dose-ranging study was designed to determine the efficacy of a non-steroidal anti-inflammatory drug, ibuprofen (IBU), and a methylxanthine, pentoxifylline (PTX). These drugs were tested singly and in combination to treat phosgene-induced acute lung injury in rats. Ibuprofen, in concentrations of 15-300 mg kg-1 (i.p.), was administered to rats 30 min before and 1 h after the start of whole-body exposure to phosgene (80 mg m-3 for 20 min). Pentoxifylline, 10-120 mg kg-1 (i.p.), was first administered 15 min prior to phosgene exposure and twice more at 45 and 105 min after the start of exposure. Five hours after phosgene inhalation, rats were euthanized, the lungs were removed and wet weight values were determined gravimetrically. Ibuprofen administered alone significantly decreased lung wet weight to body weight ratios compared with controls (P < or = 0.01) whereas PTX, at all doses tested alone, did not. In addition, the decrease in lung wet weight to body weight ratio observed with IBU+PTX could be attributed entirely to the dose of IBU employed. This is the first study to show that pre- and post-treatment with IBU can significantly reduce lung edema in rats exposed to phosgene.

Tolerance to phosgene is associated with a neutrophilic influx into the rat lung.

Exposures to 100% oxygen, ozone, nitrogen oxides, and phosgene increase both lung lavage protein concentrations and neutrophils. The inhibition of the neutrophil influx can diminish lavage protein concentrations after exposures to these oxidant gases. Similarly, this injury can be reduced by pre-exposure to either the same (tolerance) or a different (cross-tolerance) oxidant gas. We tested the hypothesis that diminished injury after the development of tolerance of phosgene (COCl2) is associated with a decreased incursion of neutrophils. Sixty-day-old rats (n=12/group) were exposed to varying concentrations of COCl2. Lung lavage (n = 6/group) 24 h after a first phosgene exposure demonstrated an increase in both protein concentrations and percentage neutrophils. The remaining animals (n = 6/group) were exposed to COCl2 2 ppm x 60 min 1 wk later. Lavage confirmed the development of tolerance with protein concentrations diminished after the second exposure in those rats that had inhaled higher doses of COCl2 during the first exposure. However, the neutrophilic influx was not diminished but rather was increased. The association of the neutrophil incursion with a protective effect was further established in studies employing colchicine and dextran. Colchicine decreased neutrophil influx occurring after the first exposure and subsequently diminished the development of tolerance after a second exposure. Intratracheal instillation of dextran produced a neutrophil incursion and subsequently decreased injury after a phosgene exposure. In investigations using both colchicine and dextran, neutrophil influx increased with the development of adaptation. Thus, lung injury after the development of tolerance to phosgene provides a unique animal model of a respiratory distress syndrome in which neutrophils are not associated with injury but rather with a protective effect.

Enhanced and prolonged pulmonary influenza virus infection following phosgene inhalation.

Animal infectivity models have been important in the demonstration of enhanced susceptibility to viral and bacterial infection as a result of low-level toxicant exposure. This study demonstrated an enhanced and prolonged viral infection using an influenza virus infectivity model in the rat following exposure to the toxicant gas phosgene. Fischer-344 rats exposed to either air or a sublethal concentration of phosgene demonstrated peak pulmonary influenza virus titers 1 d after infection. Virus titers in rats exposed to air declined rapidly falling below detectable levels by 4 d after infection. However, a significantly enhanced and prolonged pulmonary influenza virus infection was observed on d 3 and 4 after infection in rats exposed to phosgene. Virus was cleared below detectable limits on d 5 after infection in animals exposed to phosgene. Thus, inhalation of sublethal concentrations of phosgene resulted in an increased severity of pulmonary influenza virus infection. This study provides a demonstration of the effective use of a rat viral infectivity model to detect the immunotoxicity of inhaled pollutants. This model will allow future studies to focus on the immunological mechanism(s) responsible for the enhanced and prolonged pulmonary influenza virus infection.

Reduction of neutrophil influx diminishes lung injury and mortality following phosgene inhalation.

Phosgene inhalation causes a severe noncardiogenic pulmonary edema characterized by an influx of neutrophils into the lung. To study the role of neutrophils in lung injury and mortality after phosgene, we investigated the effects of leukocyte depletion with cyclophosphamide, inhibiting the generation of the chemotaxin leukotriene B4 with the 5-lipoxygenase inhibitor AA861 and impairing neutrophil migration with the microtubular poison colchicine. Cyclophosphamide, AA861, and colchicine injected before exposure significantly reduced percent neutrophils, protein, and thiobarbituric acid-reactive products in bronchoalveolar lavage fluid of rats exposed to phosgene (0.5 ppm X 60 min). Cyclophosphamide, AA861, and colchicine also significantly decreased mortality from phosgene (2.0 ppm X 90 min) in mice. Colchicine significantly reduced neutrophil influx, lung injury, and mortality even when given 30 min after phosgene exposure. We conclude that lung injury and mortality after phosgene exposure are associated with an influx of neutrophils into the lung. Prevention of neutrophil migration with colchicine may hold therapeutic potential in phosgene poisoning.

Estimation of the LCt50 of phosgene in sheep.

In all species previously studied, inhalation of toxic doses of phosgene results in varying degrees of pulmonary edema, often after a symptom-free period. The sheep is an anatomically unique animal in which to study the development of pulmonary edema by monitoring the effluent from a catheterized caudal mediastinal lymph node. In addition, the size of the sheep is sufficient to permit placement of vascular monitoring devices and withdrawal of multiple biologic samples for analyses. In spite of this, there appear to be no published reports of sheep having ever been exposed to phosgene. This study was undertaken as a dose-ranging study, in order to permit subsequent studies of phosgene inhalation toxicity in a sheep lung lymph preparation. Accordingly, the LCt50 (24 hours) was estimated to be 13,300 mg.min/m3 (3325 ppm) by "up and down" subsequent dosage selection and moving average interpolation methods.

Natural killer activity in Fischer-344 rat lungs as a method to assess pulmonary immunocompetence: immunosuppression by phosgene inhalation.

Phosgene, also known as carbonyl chloride, carbon oxychloride, and chloroformyl chloride, is a toxic air pollutant and a potential occupational health hazard. Studies were initiated (a) to evaluate the measurement of pulmonary natural killer (NK) activity as a method to assess pulmonary immunocompetence, and (b) to determine whether exposure to phosgene resulted in local pulmonary or systemic immune dysfunction. Fischer-344 male rats were exposed either to filtered air or to 1.0 ppm phosgene gas for four hours. The effect of phosgene on lung NK activity was quantified at different times after acute phosgene exposure. Pulmonary NK activity was measured by mincing lung tissue into small pieces prior to incubation with collagenase. Whole-lung homogenate was assayed for NK activity utilizing a 4 hour 51-Cr-release assay with YAC-1 cells as target cells. Acute phosgene exposure resulted in a suppressed pulmonary NK activity on days 1, 2, and 4 after exposure; however, normal levels of biological activity were observed 7 days after exposure. The suppressed NK activity was not restored after removal of adherent cells from the lung homogenate, thus indicating that the effect of phosgene on NK activity was not due to immunosuppression via mobilization of suppressor alveolar macrophages. Pulmonary immunotoxicity was also observed after exposure at 0.5 ppm, while no adverse effects were observed at 0.1 ppm phosgene. Systemic immunotoxic effects were observed for NK activity in the spleen, but not in the peripheral blood. It is thus important in pulmonary immunotoxicology to evaluate systemic immune functions, since secondary effects--distant to the original interaction--may occur with potentially serious consequences. Cells exhibiting natural killer activity comprise a part of the nonspecific innate immunity that is important in defense against both neoplastic and viral diseases. Any perturbation of this important nonspecific immunological mechanism may result in a compromised host more susceptible to infectious and neoplastic disease.