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

Countermeasures against Pulmonary Threat Agents

Inhaled toxicants are used for diverse purposes, ranging from industrial applications such as agriculture, sanitation, and fumigation to crowd control and chemical warfare, and acute exposure can induce lasting respiratory complications. The intentional release of chemical warfare agents (CWAs) during World War I caused life-long damage for survivors, and CWA use is outlawed by international treaties. However, in the past two decades, chemical warfare use has surged in the Middle East and Eastern Europe, with a shift toward lung toxicants. The potential use of industrial and agricultural chemicals in rogue activities is a major concern as they are often stored and transported near populated areas, where intentional or accidental release can cause severe injuries and fatalities. Despite laws and regulatory agencies that regulate use, storage, transport, emissions, and disposal, inhalational exposures continue to cause lasting lung injury. Industrial irritants (e.g., ammonia) aggravate the upper respiratory tract, causing pneumonitis, bronchoconstriction, and dyspnea. Irritant gases (e.g., acrolein, chloropicrin) affect epithelial barrier integrity and cause tissue damage through reactive intermediates or by direct adduction of cysteine-rich proteins. Symptoms of CWAs (e.g., chlorine gas, phosgene, sulfur mustard) progress from airway obstruction and pulmonary edema to acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), which results in respiratory depression days later. Emergency treatment is limited to supportive care using bronchodilators to control airway constriction and rescue with mechanical ventilation to improve gas exchange. Complications from acute exposure can promote obstructive lung disease and/or pulmonary fibrosis, which require long-term clinical care. SIGNIFICANCE STATEMENT: Inhaled chemical threats are of growing concern in both civilian and military settings, and there is an increased need to reduce acute lung injury and delayed clinical complications from exposures. This minireview highlights our current understanding of acute toxicity and pathophysiology of a select number of chemicals of concern. It discusses potential early-stage therapeutic development as well as challenges in developing countermeasures applicable for administration in mass casualty situations.

Synthetic and mechanistic study on the conjugate isothiocyanation of enones with trimethylsilyl isothiocyanate

Alkyl isothiocyanates (R-NCS) have pharmacological applications and provide a synthetic handle to various functional groups including thioureas. There are however few methods to access alkyl isothiocyanates through the creation of the C-N bond. We have developed a simple approach for the conjugate isothiocyanation of enones by trimethylsilyl isothiocyanate (TMSNCS), which proceeds through the 1,4-addition of the weak isothiocyanate nucleophile to activated enones in the absence of external promoters. This method avoids the direct use of highly toxic acids and bases, produces β-isothiocyanato carbonyl products in yields of 87-98% under mild conditions (less than 6 hours at 0 °C), and displays wide functional group tolerance. Density functional theory calculations highlighted competing cationic and anionic mechanisms, where the enone activation by the TMSNCS reagent is accelerated in protic solvents. The selective formation of the isothiocyanate vs. thiocyanate isomers is explained by the thermodynamically-controlled nature of the reaction in which only the conjugate isothiocyanation is exergonic.

Pentoxifylline inhibits phosgene-induced lung injury via improving hypoxia

Inhalation of high concentrations of phosgene often causes pulmonary edema, which obstructs the airway and causes tissue hypoxia. There is currently no specific antidote. This study was performed to investigate the effect behind pentoxifylline (PTX) treatment for phosgene-induced lung injury in rat models. Rats were exposed to phosgene. The protein levels of hypoxia-inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF), and occludin proteins in lung tissue were determined. The effect of both prophylactic and therapeutic administration of PTX (50 mg/kg and 100 mg/kg) was evaluated. The lung permeability index and HIF-1α protein level increased, the arterial blood oxygenation index (PaO2/FIO2 ratio) and occludin protein level decreased significantly 6 h after phosgene exposure (P < 0.05). PTX exerted protective effects by HIF-1α-VEGF-occludin signaling pathway to some extent. Moreover, prophylactic, but not therapeutic administration of PTX (100 mg/kg), exhibited a significant protective effect. Pretreatment with PTX protected against phosgene-induced lung injury, possibly by inhibiting differential expression of HIF-1α, VEGF, and occludin.

Alpha-1 antitrypsin protects against phosgene-induced acute lung injury by activating the ID1-dependent anti-inflammatory response

Phosgene is widely used as an industrial chemical, and phosgene inhalation causes acute lung injury (ALI), which may further progress into pulmonary edema. Currently, an antidote for phosgene poisoning is not known. Alpha-1 antitrypsin (α1-AT) is a protease inhibitor used to treat patients with emphysema who are deficient in α1-AT. Recent studies have revealed that α1-AT has both anti-inflammatory and anti-SARS-CoV-2 effects. Herein, we aimed to investigate the role of α1-AT in phosgene-induced ALI. We observed a time-dependent increase in α1-AT expression and secretion in the lungs of rats exposed to phosgene. Notably, α1-AT was derived from neutrophils but not from macrophages or alveolar type II cells. Moreover, α1-AT knockdown aggravated phosgene- and lipopolysaccharide (LPS)-induced inflammation and cell death in human bronchial epithelial cells (BEAS-2B). Conversely, α1-AT administration suppressed the inflammatory response and prevented death in LPS- and phosgene-exposed BEAS-2B cells. Furthermore, α1-AT treatment increased the inhibitor of DNA binding 1 (ID1) gene expression, which suppressed NF-κB pathway activation, reduced inflammation, and inhibited cell death. These data demonstrate that neutrophil-derived α1-AT acts as a self-protective mechanism, which protects against phosgene-induced ALI by activating the ID1-dependent anti-inflammatory response. This study may provide novel strategies for the treatment of patients with phosgene-induced ALI.

Lipase-mediated flow synthesis of nature-inspired phenolic carbonates

A facile and convenient lipase-catalyzed flow approach for the chemoselective synthesis of tyrosol and hydroxytyrosol methyl carbonates has been developed in neat dimethylcarbonate. The products were obtained in quantitative yield with high catalyst productivity. The biocatalytic approach was then exploited for the preparation of value-added symmetrical tyrosol and hydroxytyrosol carbonates.

PTTG1 promotes CD34+CD45+ cells to repair the pulmonary vascular barrier via activating the VEGF-bFGF/PI3K/AKT/eNOS signaling pathway in rats with phosgene-induced acute lung injury

Accidental exposure to phosgene can cause acute lung injury (ALI), characterized by uncontrolled inflammation and impaired lung blood-gas barrier. CD34⁺CD45⁺ cells with high pituitary tumor transforming gene 1 (PTTG1) expression were identified around rat pulmonary vessels through single-cell RNA sequencing, and have been shown to attenuate P-ALI by promoting lung vascular barrier repair. As a transcription factor closely related to angiogenesis, whether PTTG1 plays a role in CD34⁺CD45⁺ cell repairing the pulmonary vascular barrier in rats with P-ALI remains unclear. This study provided compelling evidence that CD34⁺CD45⁺ cells possess endothelial differentiation potential. Rats with P-ALI were intratracheally administered with CD34⁺CD45⁺ cells transfected with or without PTTG1-overexpressing and sh-PTTG1 lentivirus. It was found that CD34⁺CD45⁺ cells reduced the pulmonary vascular permeability and mitigated the lung inflammation, which could be reversed by knocking down PTTG1. Although PTTG1 overexpression enhanced the ability of CD34⁺CD45⁺ cells to attenuate P-ALI, no significant difference was found. PTTG1 was found to regulate the endothelial differentiation of CD34⁺CD45⁺ cells. In addition, knocking down of PTTG1 significantly reduced the protein levels of VEGF and bFGF, as well as their receptors, which in turn inhibited the activation of the PI3K/AKT/eNOS signaling pathway in CD34⁺CD45⁺ cells. Moreover, LY294002 (PI3K inhibitor) treatment inhibited the endothelial differentiation of CD34⁺CD45⁺ cells, while SC79 (AKT activator) yielded the opposite effect. These findings suggest that PTTG1 can promote the endothelial differentiation of CD34⁺CD45⁺ cells by activating the VEGF-bFGF/PI3K/AKT/eNOS signaling pathway, leading to the repair of the pulmonary vascular barrier in rats with P-ALI.

Identification of phytochemical compounds of Fagopyrum dibotrys and their targets by metabolomics, network pharmacology and molecular docking studies

Acute lung injury (ALI) is a clinically severe lung illness with high incidence rate and mortality. Especially, coronavirus disease 2019 (COVID-19) poses a serious threat to world wide governmental fitness. It has distributed to almost from corner to corner of the universe, and the situation in the prevention and control of COVID-19 remains grave. Traditional Chinese medicine plays a vital role in the precaution and therapy of sicknesses. At present, there is a lack of drugs for treating these diseases, so it is necessary to develop drugs for treating COVID-19 related ALI. Fagopyrum dibotrys (D. Don) Hara is an annual plant of the Polygonaceae family and one of the long-history used traditional medicine in China. In recent years, its rhizomes (medicinal parts) have attracted the attention of scholars at home and abroad due to their significant anti-inflammatory, antibacterial and anticancer activities. It can work on SARS-COV-2 with numerous components, targets, and pathways, and has a certain effect on coronavirus disease 2019 (COVID-19) related acute lung injury (ALI). However, there are few systematic studies on its aerial parts (including stems and leaves) and its potential therapeutic mechanism has not been studied. The phytochemical constituents of rhizome of F. dibotrys were collected using TCMSP database. And metabolites of F. dibotrys' s aerial parts were detected by metabonomics. The phytochemical targets of F. dibotrys were predicted by the PharmMapper website tool. COVID-19 and ALI-related genes were retrieved from GeneCards. Cross targets and active phytochemicals of COVID-19 and ALI related genes in F. dibotrys were enriched by gene ontology (GO) and KEGG by metscape bioinformatics tools. The interplay network entre active phytochemicals and anti COVID-19 and ALI targets was established and broke down using Cytoscape software. Discovery Studio (version 2019) was used to perform molecular docking of crux active plant chemicals with anti COVID-19 and ALI targets. We identified 1136 chemicals from the aerial parts of F. dibotrys, among which 47 were active flavonoids and phenolic chemicals. A total of 61 chemicals were searched from the rhizome of F. dibotrys, and 15 of them were active chemicals. So there are 6 commonly key active chemicals at the aerial parts and the rhizome of F. dibotrys, 89 these phytochemicals's potential targets, and 211 COVID-19 and ALI related genes. GO enrichment bespoken that F. dibotrys might be involved in influencing gene targets contained numerous biological processes, for instance, negative regulation of megakaryocyte differentiation, regulation of DNA metabolic process, which could be put down to its anti COVID-19 associated ALI effects. KEGG pathway indicated that viral carcinogenesis, spliceosome, salmonella infection, coronavirus disease - COVID-19, legionellosis and human immunodeficiency virus 1 infection pathway are the primary pathways obsessed in the anti COVID-19 associated ALI effects of F. dibotrys. Molecular docking confirmed that the 6 critical active phytochemicals of F. dibotrys, such as luteolin, (+) -epicatechin, quercetin, isorhamnetin, (+) -catechin, and (-) -catechin gallate, can combine with kernel therapeutic targets NEDD8, SRPK1, DCUN1D1, and PARP1. In vitro activity experiments showed that the total antioxidant capacity of the aerial parts and rhizomes of F. dibotrys increased with the increase of concentration in a certain range. In addition, as a whole, the antioxidant capacity of the aerial part of F. dibotrys was stronger than that of the rhizome. Our research afford cues for farther exploration of the anti COVID-19 associated ALI chemical compositions and mechanisms of F. dibotrys and afford scientific foundation for progressing modern anti COVID-19 associated ALI drugs based on phytochemicals in F. dibotrys. We also fully developed the medicinal value of F. dibotrys' s aerial parts, which can effectively avoid the waste of resources. Meanwhile, our work provides a new strategy for integrating metabonomics, network pharmacology, and molecular docking techniques which was an efficient way for recognizing effective constituents and mechanisms valid to the pharmacologic actions of traditional Chinese medicine.

[The role of the pulmonologist in an armed conflict]

INTRODUCTION

Recent news points to the eventuality of an armed conflict on the national territory.

STATE OF THE ART

In this situation, pulmonologists will in all likelihood have a major role to assume in caring for the injured, especially insofar as chest damage is a major cause of patient death.

PERSPECTIVES

The main injuries that pulmonologists may be called upon to treat stem not only from explosions, but also from chemical, biological and nuclear hazards. In this article, relevant organizational and pedagogical aspects are addressed. Since exhaustiveness on this subject is unattainable, we are proposing training on specific subjects for interested practitioners.

CONCLUSION

The resilience of the French health system in a situation of armed conflict depends on the active participation of all concerned parties. With this in mind, it is of prime importance that the pneumological community be sensitized to the potential predictable severity of war-related injuries.

Pulmonary Fibrosis as a Result of Acute Lung Inflammation: Molecular Mechanisms, Relevant In Vivo Models, Prognostic and Therapeutic Approaches

Pulmonary fibrosis is a chronic progressive lung disease that steadily leads to lung architecture disruption and respiratory failure. The development of pulmonary fibrosis is mostly the result of previous acute lung inflammation, caused by a wide variety of etiological factors, not resolved over time and causing the deposition of fibrotic tissue in the lungs. Despite a long history of study and good coverage of the problem in the scientific literature, the effective therapeutic approaches for pulmonary fibrosis treatment are currently lacking. Thus, the study of the molecular mechanisms underlying the transition from acute lung inflammation to pulmonary fibrosis, and the search for new molecular markers and promising therapeutic targets to prevent pulmonary fibrosis development, remain highly relevant tasks. This review focuses on the etiology, pathogenesis, morphological characteristics and outcomes of acute lung inflammation as a precursor of pulmonary fibrosis; the pathomorphological changes in the lungs during fibrosis development; the known molecular mechanisms and key players of the signaling pathways mediating acute lung inflammation and pulmonary fibrosis, as well as the characteristics of the most common in vivo models of these processes. Moreover, the prognostic markers of acute lung injury severity and pulmonary fibrosis development as well as approved and potential therapeutic approaches suppressing the transition from acute lung inflammation to fibrosis are discussed.

A Rapid, Highly Sensitive and Selective Phosgene Sensor Based on 5,6-Pinenepyridine

The toxicity of phosgene (COCl₂ ) combined with its extensive use as a reactant and building block in the chemical industry make its fast and accurate detection a prerequisite. We have developed a carboxylic derivative of 5,6-pinenepyridine which is able to act as colorimetric and fluorimetric sensor for phosgene in air and solution. For the first time, the formation of a pyrido-[2,1-a]isoindolone was used for this purpose. In solution, the sensing reaction is extremely fast (under 5 s), selective and highly sensitive, with a limit of detection (LOD) of 9.7 nM/0.8 ppb. When fixed on a solid support, the sensor is able to detect the presence of gaseous phosgene down to concentrations of 0.1 ppm, one of the lowest values reported to date.

Phosgene-Induced acute lung injury: Approaches for mechanism-based treatment strategies

Phosgene (COCl2) gas is a chemical intermediate of high-volume production with numerous industrial applications worldwide. Due to its high toxicity, accidental exposure to phosgene leads to various chemical injuries, primarily resulting in chemical-induced lung injury due to inhalation. Initially, the illness is mild and presents as coughing, chest tightness, and wheezing; however, within a few hours, symptoms progress to chronic respiratory depression, refractory pulmonary edema, dyspnea, and hypoxemia, which may contribute to acute respiratory distress syndrome or even death in severe cases. Despite rapid advances in medicine, effective treatments for phosgene-inhaled poisoning are lacking. Elucidating the pathophysiology and pathogenesis of acute inhalation toxicity caused by phosgene is necessary for the development of appropriate therapeutics. In this review, we discuss extant literature on relevant mechanisms and therapeutic strategies to highlight novel ideas for the treatment of phosgene-induced acute lung injury.

Derivation of thresholds for inhaled chemically reactive irritants: Searching for substance-specific common denominators for read-across prediction

Emergency response planning guideline values are used to protect the public when there has been a short-term chemical release. These values serve the purpose of identifying areas where a hazard exists if the concentration of hazardous chemicals is exceeded for the specified exposure duration. This paper focuses on carbonyl chlorides, a class of highly irritant/corrosive chemical intermediates characterized by the reactive moiety R-COCl. Despite their unifying property of reacting with nucleophilic biopolymers/peptides lining the airways of the respiratory tract, their adverse outcome pathway (AOP), in addition to surface area dose, appears to be dominated by their site(s) of major deposition (liquid) or retention (gas) within the respiratory tract. Thus, the physicochemical properties "phase" and "lipophilicity" become more decisive for the AOP than the chemical structure. This complicates the grouping of portal-of-entry irritant chemicals for the read-across prediction of chemicals, especially those with semivolatile properties. Phosgene (COCl₂) served as a template to predict emergency response planning levels 2 (non-incapacitating, reversible injury) and 3 (nonlethal) for related chemicals such as SOCl₂, formates, and acid chlorides. A rationale and guide to the systematic characterization of uncertainties associated with the lung region, water solubility of the vapor phase, and chemical specificity is given. The approach described in this paper highlights the regional differences and outcomes that are phenotypically described as irritation of the respiratory tract. Especially for such a data-lean group of chemicals, reliable read-across predictions could reduce the uncertainty associated with the derivation of values used for emergency-related risk assessment and management. Likewise, the approach suggested could improve the grouping and categorization of such chemicals, providing a means to reduce animal testing with potentially corrosive chemicals. Overall, the course taken for read-across predictions provided valid estimates as long as emphasis was directed to the physicochemical properties determining the most critical regional injury within the respiratory tract.

Core genes involved in the regulation of acute lung injury and their association with COVID-19 and tumor progression: A bioinformatics and experimental study

Acute lung injury (ALI) is a specific form of lung damage caused by different infectious and non-infectious agents, including SARS-CoV-2, leading to severe respiratory and systemic inflammation. To gain deeper insight into the molecular mechanisms behind ALI and to identify core elements of the regulatory network associated with this pathology, key genes involved in the regulation of the acute lung inflammatory response (Il6, Ccl2, Cat, Serpine1, Eln, Timp1, Ptx3, Socs3) were revealed using comprehensive bioinformatics analysis of whole-genome microarray datasets, functional annotation of differentially expressed genes (DEGs), reconstruction of protein-protein interaction networks and text mining. The bioinformatics data were validated using a murine model of LPS-induced ALI; changes in the gene expression patterns were assessed during ALI progression and prevention by anti-inflammatory therapy with dexamethasone and the semisynthetic triterpenoid soloxolone methyl (SM), two agents with different mechanisms of action. Analysis showed that 7 of 8 revealed ALI-related genes were susceptible to LPS challenge (up-regulation: Il6, Ccl2, Cat, Serpine1, Eln, Timp1, Socs3; down-regulation: Cat) and their expression was reversed by the pre-treatment of mice with both anti-inflammatory agents. Furthermore, ALI-associated nodal genes were analysed with respect to SARS-CoV-2 infection and lung cancers. The overlap with DEGs identified in postmortem lung tissues from COVID-19 patients revealed genes (Saa1, Rsad2, Ifi44, Rtp4, Mmp8) that (a) showed a high degree centrality in the COVID-19-related regulatory network, (b) were up-regulated in murine lungs after LPS administration, and (c) were susceptible to anti-inflammatory therapy. Analysis of ALI-associated key genes using The Cancer Genome Atlas showed their correlation with poor survival in patients with lung neoplasias (Ptx3, Timp1, Serpine1, Plaur). Taken together, a number of key genes playing a core function in the regulation of lung inflammation were found, which can serve both as promising therapeutic targets and molecular markers to control lung ailments, including COVID-19-associated ALI.

Mechanism of Phosgene-Induced Acute Lung Injury and Treatment Strategy

Phosgene (COCl₂) was once used as a classic suffocation poison and currently plays an essential role in industrial production. Due to its high toxicity, the problem of poisoning caused by leakage during production, storage, and use cannot be ignored. Phosgene mainly acts on the lungs, causing long-lasting respiratory depression, refractory pulmonary edema, and other related lung injuries, which may cause acute respiratory distress syndrome or even death in severe cases. Due to the high mortality, poor prognosis, and frequent sequelae, targeted therapies for phosgene exposure are needed. However, there is currently no specific antidote for phosgene poisoning. This paper reviews the literature on the mechanism and treatment strategies to explore new ideas for the treatment of phosgene poisoning.

Adsorption and dissociation of COCl2 on the rutile TiO2(110) surfaces: a systematic first-principles study

The adsorption and dissociation of phosgene (COCl₂) molecules on three kinds of rutile TiO₂(110) surfaces (stoichiometric: TiO₂-Sto; oxygen defective: TiO₂-Ov; and substoichiometric: TiO_1.875) were investigated based on density functional theory calculations. The nature of interactions between the COCl₂ molecule and rutile TiO₂(110) surfaces with different degrees of reduction was researched by the analysis of geometries, electron density difference, adsorption energies and density of states (DOS). Computational results show that COCl₂ indicates instability and will dissociate directly without the presence of transition states on a substoichiometric TiO_1.875(110) surface. The adsorption and dissociation behavior of COCl₂ on the rutile surface is not only helpful in providing theoretical support for the clean and efficient degradation of COCl₂, but also helpful in elucidating the role of COCl₂ as an intermediate product in the carbochlorination of titanium ore.

Human risk assessment of inhaled irritants: Role of sensory stimulations from spatially separated nociceptors

Contemporary approaches to human health risk assessment for respiratory tract irritants are variable and controversial. This manuscript provides an in-depth analysis and assessment of the applicability of the classical respiratory depression 50 % (RD₅₀) assay with focus on the Log-linear extrapolation of the non-sensory irritant threshold (RD₀ or RD₁₀) relative to the contemporary Point of Departure (POD) U.S.-EPA benchmark approach. Three prototypic volatile chemically reactive irritants are used to exemplify the pros and cons of this alternative approach. These irritants differ in physicochemical properties affecting water-solubility and lipophilicity. Depending on these variables, a vapor may preferentially be retained in the extrathoracic region (ET), the tracheobronchial region (TB), and the pulmonary region (PU); although a smooth transition between these regions occurs at increasingly high concentrations. Each region has its specific nociceptors sensing irritants and regional-specific response to injury. The alternative approach using rats identified the chemical-specific critical region of respiratory tract injury. Statistically derived PODs on ET-TB related sensory irritation provide important information for ET-TB irritants but not for PU irritants. The POD of ET-TB irritants from acute and repeated studies decreased substantially. In summary, statistically derived PODs improve the risk assessment of respiratory tract irritants; however, those from repeated exposures should be given preference to those from acute exposures.