Formation of chlorinated lipids post-chlorine gas exposure

The long road to Ithaca: a physiologist's journey

It was an honor to be asked to deliver the Walter B. Cannon Lecture during the 2024 American Physiological Summit meeting. Dr. Cannon served as president of the American Physiological Society from 1914-1916. He coined the term "fight or flight" to describe an animal's response to threats and the concept of Homeostasis. He was the consummate physician-scientist, an outstanding mentor and teacher, a prolific writer, and a humanitarian. The title of my lecture is based on a poem entitled "Ithaca," written by the Greek poet C. P. Cavafy, who recounts the 10 yr travels of Ulysses, from Troy to his home, Ithaca. Odysseus had to overcome many obstacles to survive this long journey. Like Odysseus, I encountered myriad of professional and health problems. But, I also have experienced the thrill of contributing to scientific knowledge, the satisfaction of watching my mentees develop into independent scientists, the excitement of teaching respiration physiology to medical and professional students, and the pleasure of being of service to my discipline by serving as Editor of the American Journal of Physiology-Lung Cellular and Molecular Physiology and of Physiological Reviews. During my career, I have been interested in identifying the basic mechanisms by which oxidant gases and pathogens damage the blood gas barrier resulting in acute and chronic lung injury. In this brief review, I summarize the results of current studies implicating free heme as a major mediator of acute lung injury and our efforts to develop recombinant forms of human hemopexin, as a countermeasure.

Human lung microvascular endothelial cell protein modification by 2-chlorohexadecanoic acid: RhoA mediates 2-chlorohexadecanoic acid-elicited endothelial activation

Chlorolipids are produced during the neutrophil respiratory burst as a result of myeloperoxidase (MPO)-generated hypochlorous acid (HOCl) targeting the vinyl ether bond of plasmalogen phospholipids. The initial products of this reaction are 2-chlorofatty aldehydes (2-ClFALDs), which are subsequently oxidized to 2-chlorofatty acids (2-ClFAs). 2-Chlorohexadecanoic acid (2-ClHA) is the 16-carbon 2-ClFA species, and previous studies have shown that increased levels of plasma 2-ClHA associate with acute respiratory distress syndrome (ARDS)-caused mortality in human sepsis. 2-ClHA causes endothelial barrier dysfunction and increases neutrophil and platelet adherence to the endothelium. In this study, click chemistry analogs of 2-ClHA and hexadecanoic acid (HA) were used to identify proteins covalently modified by 2-ClHA and HA in human lung microvascular endothelial cells (HLMVECs). Eleven proteins were specifically modified by 2-ClHA, and an additional one hundred and ninety-four proteins were modified by both 2-ClHA and HA. STRING analysis of 2-ClHA-modified proteins revealed a network of proteins with RhoA as a hub. RhoA is one of the proteins specifically modified by 2-ClHA and not HA. The RhoA inhibitors, Rhosin and C3, inhibited both 2-ClHA-elicited HLMVEC barrier dysfunction and angiopoietin-2 (Ang-2) release from HLMVEC. Further studies showed 2-ClHA activates HLMVEC RhoA activity. The specificity of the 2-ClHA-RhoA pathway for endothelial activation was further confirmed since HA did not cause HLMVEC barrier dysfunction, Ang-2 release and RhoA activation. Collectively, these studies have identified multiple proteins modified exclusively by 2-ClHA in HLMVECs, including RhoA. These proteomics studies led to the key finding that RhoA is an important mediator of 2-ClHA-caused endothelial barrier dysfunction.

Discovery of chlorine exposure signatures in plant material using targeted and comparative mass spectrometry methods

Recent uses of chlorine gas in violation of the Chemical Weapons Convention are difficult to identify through chemical analysis as unique signatures of exposure have not been identified. We exposed living pine seedlings and English ivy to chlorine gas, extracted the pine needles, and analyzed the extracts by liquid chromatography-time of flight mass spectrometry (LC-qTOF) and comprehensive two-dimensional gas chromatography mass spectrometry (GC×GC-TOF). Data from exposed seedlings was compared to unexposed seedlings and bleach-treated seedlings using commercial and Battelle proprietary software to identify unique or elevated markers of exposure. Battelle also used targeted mass spectrometry to evaluate 3-chlorotyrosine and 3,5-chlorotyrosine as chlorine exposure biomarkers that were expected to be present in exposed pine needles. We discovered ten (10) chlorine exposure biomarkers in chlorine gas-exposed pine needle and ivy leaf extracts using survey mass spectrometry methods. Additional survey mass spectrometry analysis suggested additional biomarkers (chlorinated glycosylated flavonoid analogs) may be present but that sufficient levels were not generated for detection in extracts from the chlorine gas-exposed samples. Targeted analysis for 3-chlorotyrosine and 3,5-dichlorotyrosine indicated presence of 3-chlorotyrosine in extracts from exposed ivy.

2-Chloro- and 2-Bromopalmitic acids inhibit mitochondrial function in airway epithelial cells

2-Chloropalmitic acid (2-ClPA) and 2-bromopalmitic acid (2-BrPa) increase in inflammatory lung disease associated with formation of hypochlorous or hypobromous acid, and exposure to halogen gases. Moreover, these lipids may elicit cell responses that contribute to lung injury, but the mechanisms remain unclear. Here, we tested the hypothesis that 2-ClPA and 2-BrPA induce metabolic defects in airway epithelial cells by targeting mitochondria. H441 or primary human airway epithelial cells were treated with 2-ClPA or 2-BrPA and bioenergetics measured using oxygen consumption rates and extracellular acidification rates, as well as respiratory complex activities. Relative to vehicle or palmitic acid, both 2-halofatty acids inhibited ATP-linked oxygen consumption and reserve capacity, suggestive of increased proton leak. However, neither 2-ClPA nor 2-BrPA altered mitochondrial membrane potential, suggesting proton leak does not underlie inhibited ATP-linked oxygen consumption. Interestingly, complex II activity was significantly inhibited which may contribute to diminished reserve capacity, but activity of complexes I, III and IV remain unchanged. Taken together, the presented data highlight the potential of 2-halofatty acids to disrupt bioenergetics and in turn cause cellular dysfunction.

Determination of biomarkers of chlorine exposure from biological samples: a review of analysis techniques

Introduction: Chlorine gas can be toxic when inhaled or absorbed at high concentrations through the skin. It can cause pulmonary edema, pulmonary inflammation, respiratory failure, and potentially death. Monitoring chlorine exposure helps in determining treatment regimens and may inform safeguards, such as personal protective equipment and ventilation systems. Therefore, verification of chlorine exposure is crucial to protecting human health. This has led to identification of multiple biomarkers of Cl2 exposure with associated innovations in methods of analysis to monitor these markers.

Materials and methods: In this review of the last 30 years of literature, biomarkers and associated methods of detection for the determination of chlorine exposure from biological samples are detailed and critically evaluated.

Results and discussion: From the 36 included studies, the most useful biomarkers for Cl2 exposure include tyrosine adducts, chlorohydrin, chloro-fatty-acids, chloro-fatty-aldehydes, and chloro-fatty-alcohols. The most common sample preparation methods for these markers are hydrolysis and extraction and the most common analysis techniques are chromatographic separation with mass spectrometric detection.

Conclusion: The findings of this review emphasize the need for continued research into biomarkers and stronger evaluation of proposed analytical methods, including validation, to allow more appropriate comparison, which will ultimately improve patient outcomes.

Surviving chlorinated waters: bleaching sensitivity and persistence of free-living amoebae

Recent advancements in membrane technologies and disinfection methods have enhanced drinking water quality significantly. However, microorganisms, including free-living amoebae (FLA), persist and pose potential threats to humans. FLA are linked to severe neuro-ophthalmic infections and serve as hosts of pathogenic bacteria. This study examined FLA presence in chlorinated and ultrafiltration drinking water and evaluated chlorine's disinfectant. Of 115 water samples, 21 tested positive for Acanthamoeba sp., Allovahlkampfia sp., and Vermamoeba vermiformis, originating from chlorinated sources. FLA trophozoites withstand temperatures up to 37 °C, while the cysts tolerate heat shocks of 60-70 °C. Trophozoites are susceptible to 5 mg L-1 chlorine, but cysts remain viable at concentrations up to 10 mg L-1. FLAs' survival in chlorinated waters is attributed to high cyst tolerance and lower residual chlorine concentrations. These findings highlight the need for ultrafiltration or enhanced chlorination protocols to ensure safer drinking water.

Myocardial SERCA2 Protects Against Cardiac Damage and Dysfunction Caused by Inhaled Bromine

Myocardial sarcoendoplasmic reticulum calcium ATPase 2 (SERCA2) activity is critical for heart function. We have demonstrated that inhaled halogen (chlorine or bromine) gases inactivate SERCA2, impair calcium homeostasis, increase proteolysis, and damage the myocardium ultimately leading to cardiac dysfunction. To further elucidate the mechanistic role of SERCA2 in halogen-induced myocardial damage, we used bromine-exposed cardiac-specific SERCA2 knockout (KO) mice [tamoxifen-administered SERCA2 (flox/flox) Tg (αMHC-MerCreMer) mice] and compared them to the oil-administered controls. We performed echocardiography and hemodynamic analysis to investigate cardiac function 24 hours after bromine (600 ppm for 30 minutes) exposure and measured cardiac injury markers in plasma and proteolytic activity in cardiac tissue and performed electron microscopy of the left ventricle (LV). Cardiac-specific SERCA2 knockout mice demonstrated enhanced toxicity to bromine. Bromine exposure increased ultrastructural damage, perturbed LV shape geometry, and demonstrated acutely increased phosphorylation of phospholamban in the KO mice. Bromine-exposed KO mice revealed significantly enhanced mean arterial pressure and sphericity index and decreased LV end diastolic diameter and LV end systolic pressure when compared with the bromine-exposed control FF mice. Strain analysis showed loss of synchronicity, evidenced by an irregular endocardial shape in systole and irregular vector orientation of contractile motion across different segments of the LV in KO mice, both at baseline and after bromine exposure. These studies underscore the critical role of myocardial SERCA2 in preserving cardiac ultrastructure and function during toxic halogen gas exposures. SIGNIFICANCE STATEMENT: Due to their increased industrial production and transportation, halogens such as chlorine and bromine pose an enhanced risk of exposure to the public. Our studies have demonstrated that inhalation of these halogens leads to the inactivation of cardiopulmonary SERCA2 and results in calcium overload. Using cardiac-specific SERCA2 KO mice, these studies further validated the role of SERCA2 in bromine-induced myocardial injury. These studies highlight the increased susceptibility of individuals with pathological loss of cardiac SERCA2 to the effects of bromine.

Biomarker profiling in plants to distinguish between exposure to chlorine gas and bleach using LC-HRMS/MS and chemometrics

Since its first employment in World War I, chlorine gas has often been used as chemical warfare agent. Unfortunately, after suspected release, it is difficult to prove the use of chlorine as a chemical weapon and unambiguous verification is still challenging. Furthermore, similar evidence can be found for exposure to chlorine gas and other, less harmful chlorinating agents. Therefore, the current study aims to use untargeted high resolution mass spectrometric analysis of chlorinated biomarkers together with machine learning techniques to be able to differentiate between exposure of plants to various chlorinating agents. Green spire (Euonymus japonicus), stinging nettle (Urtica dioica), and feathergrass (Stipa tenuifolia) were exposed to 1000 and 7500 ppm chlorine gas and household bleach, pool bleach, and concentrated sodium hypochlorite. After sample preparation and digestion, the samples were analyzed by liquid chromatography high resolution tandem mass spectrometry (LC-HRMS/MS) and liquid chromatography tandem mass spectrometry (LC-MS/MS). More than 150 chlorinated compounds including plant fatty acids, proteins, and DNA adducts were tentatively identified. Principal component analysis (PCA) and linear discriminant analysis (LDA) showed clear discrimination between chlorine gas and bleach exposure and grouping of the samples according to chlorine concentration and type of bleach. The identity of a set of novel biomarkers was confirmed using commercially available or synthetic reference standards. Chlorodopamine, dichlorodopamine, and trichlorodopamine were identified as specific markers for chlorine gas exposure. Fenclonine (Cl-Phe), 3-chlorotyrosine (Cl-Tyr), 3,5-dichlorotyrosine (di-Cl-Tyr), and 5-chlorocytosine (Cl-Cyt) were more abundantly present in plants after chlorine contact. In contrast, the DNA adduct 2-amino-6-chloropurine (Cl-Ade) was identified in both types of samples at a similar level. None of these chlorinated biomarkers were observed in untreated samples. The DNA adducts Cl-Cyt and Cl-Ade could clearly be identified even three months after the actual exposure. This study demonstrates the feasibility of forensic biomarker profiling in plants to distinguish between exposure to chlorine gas and bleach.

Recapitulation of human pathophysiology and identification of forensic biomarkers in a translational model of chlorine inhalation injury

Chlorine gas (Cl2) has been repeatedly used as a chemical weapon, first in World War I and most recently in Syria. Life-threatening Cl2 exposures frequently occur in domestic and occupational environments, and in transportation accidents. Modeling the human etiology of Cl2-induced acute lung injury (ALI), forensic biomarkers, and targeted countermeasures development have been hampered by inadequate large animal models. The objective of this study was to develop a translational model of Cl2-induced ALI in swine to understand toxico-pathophysiology and evaluate whether it is suitable for screening potential medical countermeasures and to identify biomarkers useful for forensic analysis. Specific pathogen-free Yorkshire swine (30-40 kg) of either sex were exposed to Cl2 (≤240 ppm for 1 h) or filtered air under anesthesia and controlled mechanical ventilation. Exposure to Cl2 resulted in severe hypoxia and hypoxemia, increased airway resistance and peak inspiratory pressure, and decreased dynamic lung compliance. Cl2 exposure resulted in increased total leucocyte and neutrophil counts in bronchoalveolar lavage fluid, vascular leakage, and pulmonary edema compared with the air-exposed group. The model recapitulated all three key histopathological features of human ALI, such as neutrophilic alveolitis, deposition of hyaline membranes, and formation of microthrombi. Free and lipid-bound 2-chlorofatty acids and chlorotyrosine-modified proteins (3-chloro-l-tyrosine and 3,5-dichloro-l-tyrosine) were detected in plasma and lung tissue after Cl2 exposure. In this study, we developed a translational swine model that recapitulates key features of human Cl2 inhalation injury and is suitable for testing medical countermeasures, and validated chlorinated fatty acids and protein adducts as biomarkers of Cl2 inhalation.NEW & NOTEWORTHY We established a swine model of chlorine gas-induced acute lung injury that exhibits several features of human acute lung injury and is suitable for screening potential medical countermeasures. We validated chlorinated fatty acids and protein adducts in plasma and lung samples as forensic biomarkers of chlorine inhalation.

Establishing Population Values for Chlorine Exposure in the United States (2015-2016) Using 2 Chlorine Biomarkers, 3-Chlorotyrosine and 3,5-Dichlorotyrosine

BACKGROUND

In the United States, 12 million short tons of chlorine are manufactured and transported each year. Due to the volume of this volatile chemical, large- and small-scale chemical exposures occur frequently. To diagnose and treat potentially exposed individuals, reference range values for confirmatory biomarkers are required to differentiate between normal and abnormal exposure levels.

METHODS

Serum surplus samples (n = 1780) from the National Health and Nutrition Examination Survey (NHANES) 2015-2016 were measured for 2 chlorine biomarkers, 3-chlorotyrosine (Cl-Tyr) and 3,5-dichlorotyrosine (Cl2-Tyr), by liquid chromatography coupled to a triple quadrupole mass spectrometer. We evaluated demographic factors associated with elevated biomarker levels.

RESULTS

Participant samples were analyzed for the chlorine biomarkers Cl-Tyr and Cl2-Tyr. In the unweighted analysis of these samples, 1349 (75.8%) were under the limit of detection (< LOD) of 2.50 ng/mL for Cl-Tyr and 1773 (99.6%) were < LOD for Cl2-Tyr. Samples within the method reportable range were 2.50 to 35.6 ng/mL for Cl-Tyr and 2.69 to 11.2 ng/mL for Cl2-Tyr. Since only 7 of the 1780 participants had detectable Cl2-Tyr, statistical analysis was limited to Cl-Tyr. Of the demographic characteristics examined, age, body mass index (BMI), estimated glomerular filtration rate (eGFR), and sex exhibited statistically significant differences in the weighted prevalence of detectable Cl-Tyr.

CONCLUSIONS

This is the first reported set of Cl-Tyr and Cl2-Tyr population values for the United States. This population range coupled with NHANES demographic information could help healthcare professionals distinguish between normal and abnormal chlorine biomarker levels in an emergency. With this information, an inference could be made when determining acute chlorine exposure in individuals.

Verification of chlorine exposure via LC-MS/MS analysis of base hydrolyzed chlorophenols from chlorotyrosine-protein adducts

Inhalation of chlorine gas, with subsequent hydrolysis in the airway and lungs to form hydrochloric acid (HCl) and hypochlorous acid (HOCl), can cause pulmonary edema (i.e., fluid build-up in the lungs), pulmonary inflammation (with or without infection), respiratory failure, and death. The HOCl produced from chlorine is known to react with tyrosine to form adducts via electrophilic aromatic substitution, resulting in 3-chlorotyrosine and 3,5-dichlorotyrosine adducts. While several analysis methods are available for determining these adducts, each method has significant disadvantages. Hence, a simple and sensitive ultra-high performance liquid chromatography-tandem mass spectroscopy (UHPLC-MS/MS) method was developed for the determination of chlorotyrosine adducts. The sample preparation involves base hydrolysis of isolated plasma proteins to form 2-chlorophenol (CP) from monochlorotyrosine adducts and 2,6-dichlorophenol (2,6-DCP), from dichlorotyrosine adducts, as markers of chlorine exposure. The chlorophenols are extracted with cyclohexane prior to UHPLC-MS/MS analysis. The method produced excellent sensitivity for 2,6-DCP with a limit of detection of 2.2 μg/kg, calibration curve linearity extending from 0.054-54 mg/kg (R2 ≥ 0.9997 and %RA > 94), and accuracy and precision of 100 ± 14 %, and <15 % relative standard deviation, respectively. The sensitivity of the method for 2-CP was relatively poor, so it was used only as a secondary marker for severe chlorine exposure. The method successfully detected elevated levels of 2,6-DCP from hypochlorite-spiked plasma protein and plasma protein isolated from chlorine-exposed rats.

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.

Phospholipid chlorohydrins as chlorine exposure biomarkers in a large animal model

Chlorine is a toxic industrial chemical that has been used as a chemical weapon in recent armed conflicts. Confirming human exposure to chlorine has proven challenging, and there is currently no established method for analyzing human biomedical samples to unambiguously verify chlorine exposure. In this study, two chlorine-specific biomarkers: palmitoyl-oleoyl phosphatidylglycerol chlorohydrin (POPG-HOCl) and the lipid derivative oleoyl ethanolamide chlorohydrin (OEA-HOCl) are shown in bronchoalveolar lavage fluid (BALF) samples from spontaneously breathing pigs after chlorine exposure. These biomarkers are formed by the chemical reaction of chlorine with unsaturated phospholipids found in the pulmonary surfactant, which is present at the gas-liquid interface within the lung alveoli. Our results strongly suggest that lipid chlorohydrins are promising candidate biomarkers in the development of a verification method for chlorine exposure. The establishment of verified methods capable of confirming the illicit use of toxic industrial chemicals is crucial for upholding the principles of the Chemical Weapons Convention (CWC) and enforcing the ban on chemical weapons. This study represents the first published dataset in BALF revealing chlorine biomarkers detected in a large animal. Furthermore, these biomarkers are distinct in that they originate from molecular chlorine rather than hypochlorous acid.

Characterization of N-Acetyl Cysteine Adducts with Exogenous and Neutrophil-Derived 2-Chlorofatty Aldehyde

Hypochlorous acid is produced by leukocyte myeloperoxidase activity. 2-Chlorofatty aldehydes (2-ClFALDs) are formed when hypochlorous acid attacks the plasma membrane phospholipid plasmalogen molecular subclass and are thus produced following leukocyte activation as well as in the lungs of mice exposed to chlorine gas. The biological role of 2-ClFALD is largely unknown. Recently, we used an alkyne analog (2-ClHDyA) of the 2-ClFALD molecular species, 2-chlorohexadecanal (2-ClHDA), to identify proteins covalently modified by 2-ClHDyA in endothelial cells and epithelial cells. Here, we demonstrate that 2-ClHDA reduces the metabolic activity of RAW 264.7 cells in a dose-dependent manner. 2-ClHDyA localizes to the mitochondria, endoplasmic reticulum and Golgi in RAW 264.7 cells and modifies many proteins. The thiol-containing precursor of glutathione, N-acetyl cysteine (NAC), was shown to produce an adduct with 2-ClHDA with the loss of Cl^- (HDA-NAC). This adduct was characterized in both positive and negative ion modes using LC-MS/MS and electrospray ionization. NAC treatment of neutrophils reduced the 2-ClFALD levels in PMA-stimulated cells with subsequent increases in HDA-NAC. NAC treatments reduced the 2-ClHDA-elicited loss of metabolic activity in RAW 264.7 cells as well as 2-ClHDA protein modification. These studies demonstrate that 2-ClFALD toxic effects can be reduced by NAC, which reduces protein modification.

Myeloperoxidase-derived hypochlorous acid targets human airway epithelial plasmalogens liberating protein modifying electrophilic 2-chlorofatty aldehydes

Neutrophil and airway epithelial cell interactions are critical in the inflammatory response to viral infections including respiratory syncytial virus, Sendai virus, and SARS-CoV-2. Airway epithelial cell dysfunction during viral infections is likely mediated by the interaction of virus and recruited neutrophils at the airway epithelial barrier. Neutrophils are key early responders to viral infection. Neutrophil myeloperoxidase catalyzes the conversion of hydrogen peroxide to hypochlorous acid (HOCl). Previous studies have shown HOCl targets host neutrophil and endothelial cell plasmalogen lipids, resulting in the production of the chlorinated lipid, 2-chlorofatty aldehyde (2-ClFALD). We have previously shown that the oxidation product of 2-ClFALD, 2-chlorofatty acid (2-ClFA) is present in bronchoalveolar lavage fluid of Sendai virus-infected mice, which likely results from the attack of the epithelial plasmalogen by neutrophil-derived HOCl. Herein, we demonstrate small airway epithelial cells contain plasmalogens enriched with oleic acid at the sn-2 position unlike endothelial cells which contain arachidonic acid enrichment at the sn-2 position of plasmalogen. We also show neutrophil-derived HOCl targets epithelial cell plasmalogens to produce 2-ClFALD. Further, proteomics and over-representation analysis using the ω-alkyne analog of the 2-ClFALD molecular species, 2-chlorohexadecanal (2-ClHDyA) showed cell adhesion molecule binding and cell-cell junction enriched categories similar to that observed previously in endothelial cells. However, in contrast to endothelial cells, proteins in distinct metabolic pathways were enriched with 2-ClFALD modification, particularly pyruvate metabolism was enriched in epithelial cells and mitochondrial pyruvate respiration was reduced. Collectively, these studies demonstrate, for the first time, a novel plasmalogen molecular species distribution in airway epithelial cells that are targeted by myeloperoxidase-derived hypochlorous acid resulting in electrophilic 2-ClFALD, which potentially modifies epithelial physiology by modifying proteins.

Elucidation of in Vitro Chlorinated Tyrosine Adducts in Blood Plasma as Selective Biomarkers of Chlorine Exposure

Chlorine is a widely available industrial chemical and involved in a substantial number of cases of poisoning. It has also been used as a chemical warfare agent in military conflicts. To enable forensic verification, the persistent biomarkers 3-chlorotyrosine and 3,5-dichlorotyrosine in biomedical samples could be detected. An important shortfall of these biomarkers, however, is the relatively high incidence of elevated levels of chlorinated tyrosine residues in individuals with inflammatory diseases who have not been exposed to chlorine. Therefore, more reliable biomarkers are necessary to distinguish between endogenous formation and exogeneous exposure. The present study aims to develop a novel diagnostic tool for identifying site-specific chlorinated peptides as a more unambiguous indicator of exogeneous chlorine exposure. Human blood plasma was exposed in vitro to various chlorine concentrations, and the plasma proteins were subsequently digested by pronase, trypsin, or pepsin. After sample preparation, the digests were analyzed by liquid chromatography tandem mass spectrometry (LC-MS/MS) and liquid chromatography high-resolution tandem mass spectrometry (LC-HRMS/MS). In line with other studies, low levels of 3-chlorotyrosine and 3,5-dichlorotyrosine were found in blank plasma samples in this study. Therefore, 50 site-specific biomarkers were identified, which could be used as more unambiguous biomarkers for chlorine exposure. Chlorination of the peptides TY*ETTLEK, Y*KPGQTVK, Y*QQKPGQAPR, HY*EGSTVPEK, and Y*LY*EIAR could already be detected at moderate in vitro chlorine exposure levels. In addition, the latter two peptides were found to have dichlorinated fragments. Especially, Y*LY*EIAR, with a distinct chlorination pattern in the MS spectra, could potentially be used to differentiate exogeneous exposure from endogenous causes as other studies reported that this part of human serum albumin is nitrated rather than chlorinated under physiological conditions. In conclusion, trypsin digestion combined with high-resolution MS analysis of chlorinated peptides could constitute a valuable technique for the forensic verification of exposure to chlorine.

Endothelial Cell Protein Targeting by Myeloperoxidase-Derived 2-Chlorofatty Aldehyde

Neutrophils are important cellular mediators of injury and repair in diseases including ischemic heart disease, atherosclerosis, and sepsis. Myeloperoxidase-derived (MPO)-oxidants released from neutrophils are potential mediators of endothelial injury in disease. MPO-derived HOCl attacks plasmalogen phospholipid to liberate 2-chlorofatty aldehyde (2-ClFALD). Both 2-ClFALD and its oxidation product, 2-chlorofatty acid (2-ClFA), are electrophilic lipids, and both probably react with proteins through several mechanisms. In the present study, we investigate protein modification specifically by 2-ClFALD under non-reducing conditions (e.g., without stabilizing Schiff base bonds), which likely reflects nucleophilic targeting of the electrophilic chlorinated carbon. Protein modification by the ω-alkyne analog of 2-chlorohexadecanal (2-ClHDA), 2-ClHDyA, was compared to that with the ω-alkyne analog of 2-chlorohexadecanoic acid (2-ClHA), 2-ClHyA, in multiple cell lines, which demonstrated 2-ClFALD preferentially modifies proteins compared to 2-ClFA. The 2-ClHDyA modified proteins from EA.hy926 cells and human lung microvascular endothelial cells analyzed by shotgun proteomics and over-representation analysis included adherens junction, cell adhesion molecule binding, and cell substrate junction enrichment categories. It is possible that proteins in these groups may have roles in previously described 2-ClFALD-elicited endothelial barrier dysfunction.

Halogen-Induced Chemical Injury to the Mammalian Cardiopulmonary Systems

The halogens chlorine (Cl₂) and bromine (Br₂) are highly reactive oxidizing elements with widespread industrial applications and a history of development and use as chemical weapons. When inhaled, depending on the dose and duration of exposure, they cause acute and chronic injury to both the lungs and systemic organs that may result in the development of chronic changes (such as fibrosis) and death from cardiopulmonary failure. A number of conditions, such as viral infections, coexposure to other toxic gases, and pregnancy increase susceptibility to halogens significantly. Herein we review their danger to public health, their mechanisms of action, and the development of pharmacological agents that when administered post-exposure decrease morbidity and mortality.

Chlorine inhalation induces acute chest syndrome in humanized sickle cell mouse model and ameliorated by postexposure hemopexin

Triggering factors of Acute Chest Syndrome (ACS) is a leading cause of death in patients with Sickle Cell Disease (SCD) and targeted therapies are limited. Chlorine (Cl2) inhalation happens frequently, but its role as a potential trigger of ACS has not been determined. In this study, we hypothesized that Cl2 exposure resembling that in the vicinity of industrial accidents induces acute hemolysis with acute lung injury, reminiscent of ACS in humanized SCD mice. When exposed to Cl2 (500 ppm for 30 min), 64% of SCD mice succumbed within 6 h while none of the control mice expressing normal human hemoglobin died (p<0.01). Surviving SCD mice had evidence of acute hemolysis, respiratory acidosis, acute lung injury, and high concentrations of chlorinated palmitic and stearic acids (p<0.05) in their plasmas and RBCs compared to controls. Treatment with a single intraperitoneal dose of human hemopexin 30 min after Cl2 inhalation reduced mortality to around 15% (p<0.01) with reduced hemolysis (decreased RBCs fragility (p<0.001) and returned plasma heme to normal levels (p<0.0001)), improved oxygenation (p<0.0001) and reduced acute lung injury scores (p<0.0001). RBCs from SCD mice had significant levels of carbonylation (which predisposes RBCs to hemolysis) 6 h post-Cl2 exposure which were absent in RBCs of mice treated with hemopexin. To understand the mechanisms leading to carbonylation, we incubated RBCs from SCD mice with chlorinated lipids and identified sickling and increased hemolysis compared to RBCs obtained from control mice and treated similarly. Our study indicates that Cl2 inhalation induces ACS in SCD mice via induction of acute hemolysis, and that post exposure administration of hemopexin reduces mortality and lung injury. Our data suggest that SCD patients are vulnerable in Cl2 exposure incidents and that hemopexin is a potential therapeutic agent.

Development of an LC-MS/MS method for quantification of 3-chloro-L-tyrosine as a candidate marker of chlorine poisoning

A simple and sensitive liquid chromatography coupled with electrospray ionization-tandem mass spectrometry (LC/ESI-MS/MS) method for the determination of 3-chloro-L-tyrosine (Cl-Tyr) was developed and validated. For sample preparation, 50 μL of the body fluids or tissue extracts were processed by protein precipitation followed by the derivatization with dansyl chloride. The calibration curve was linear over the concentration range of 2.0-200 ng/mL blood or 4.0-400 ng/g tissue. Our method allowed the reproducible and accurate quantification. That is, the intra- and inter-assay coefficients of variation were below 7.73 and 6.94%, respectively in both the blood and lung. We applied the developed method to the analysis of Cl-Tyr in the human autopsy samples, which were suspected of chlorine poisoning, and detected 55.2 ng/mL and 206.6 ng/g Cl-Tyr in left heart blood and lung, respectively. Furthermore, in more than 20 autopsy samples, which were obtained from other causes of death including burn, drowning, hanging, internal disease, trauma and drug poisoning, Cl-Tyr was almost not detected in their both body fluids and organ tissues. In conclusion, the data here reported demonstrate that the LC/ESI-MS/MS method allows the Cl-Tyr in the autopsy samples and that chlorine exposure strongly affects its level, providing a basis for novel identification tool of chlorine poisoning.

Nasal Lavage Fluid as a Biomedical Sample for Verification of Chlorine Exposure

Chlorine is a toxic chemical that has been used as a chemical warfare agent in recent armed conflicts. There is an urgent need for methods to verify alleged uses of chlorine, and phospholipid chlorohydrins (PL-HOCl) derived from the pulmonary surfactant of exposed victims have previously been proposed as biomarkers of chlorine exposure. Here we describe an improved protocol for the chemical analysis of these biomarkers and its applicability to biomedical samples from chlorine-exposed animals. By the use of a polymeric solid phase-supported transesterification of PL-HOCl using ethanolamine, a common biomarker; oleoyl ethanolamide chlorohydrin (OEA-HOCl), was derived from all the diverse oleoyl PL-HOCl that may be formed by chlorine exposure. Compared to native lipid biomarkers, OEA-HOCl represents a larger biomarker pool and is better suited for nano-liquid chromatography tandem mass spectrometry (nLC-MS/MS analysis), generating 3 amol LOD and a reduced sample carry-over. With the improved protocol, significantly elevated levels of OEA-HOCl was identified in broncho-alveolar lavage fluid (BALF) of chlorine exposed rats, 2-48 hours after exposure. The difficulty of BALF sampling from humans limits the methods usefulness as a verification tool of chlorine exposure. Conversely, nasal lavage fluid (NLF) is readily collected without advanced equipment. In NLF from chlorine-exposed rats, PL-HOCl were identified and significantly elevated levels of the OEA-HOCl biomarker was detected 2- 24 hours after exposure. In order to test the potential of NLF as a biomedical sample for verification of human exposure to chlorine, in-vitro chlorination of human NLF samples was performed. All human in-vitro chlorinated NLF samples exhibited elevated OEA-HOCl biomarker levels, following sample derivatization. This data indicates the potential of human NLF as a biomedical sample for the verification of chlorine exposure but further work is required to develop and validate the method for the use on real-world samples.

Development of a clinical assay to measure chlorinated tyrosine in hair and tissue samples using a mouse chlorine inhalation exposure model

Chlorine is a toxic industrial chemical with a history of use as a chemical weapon. Chlorine is also produced, stored, and transported in bulk making it a high-priority pulmonary threat in the USA. Due to the high reactivity of chlorine, few biomarkers exist to identify exposure in clinical and environmental samples. Our laboratory evaluates acute chlorine exposure in clinical samples by measuring 3-chlorotyrosine (Cl-Tyr) and 3,5-dichlorotyrosine (Cl₂-Tyr) using liquid chromatography tandem mass spectrometry (LC-MS/MS). Individuals can have elevated biomarker levels due to their environment and chronic health conditions, but levels are significantly lower in individuals exposed to chlorine. Historically these biomarkers have been evaluated in serum, plasma, blood, and bronchoalveolar lavage (BAL) fluid. We report the expansion into hair and lung tissue samples using our newly developed tissue homogenization protocol which fits seamlessly with our current chlorinated tyrosine quantitative assay. Furthermore, we have updated the chlorinated tyrosine assay to improve throughput and ruggedness and reduce sample volume requirements. The improved assay was used to measure chlorinated tyrosine levels in 198 mice exposed to either chlorine gas or air. From this animal study, we compared Cl-Tyr and Cl₂-Tyr levels among three matrices (i.e., lung, hair, and blood) and found that hair had the most abundant chlorine exposure biomarkers. Furthermore, we captured the first timeline of each analyte in the lung, hair, and blood samples. In mice exposed to chlorine gas, both Cl-Tyr and Cl₂-Tyr were present in blood and lung samples up to 24 h and up to 30 days in hair samples.

Lessons Learned From a Chlorine Gas Leakage in Dezful City, Iran

Dezful is the capital of Dezful County, a city in Khuzestan Province, Iran. On August 12, 2017, after a chlorine gas leakage in Dezful, more than 475 people were affected by chlorine gas, and they all suffered from respiratory complications. A lot of problems were encountered in the preparation of the relief forces and organization of the blueprint on how to respond to the incident, such as lack of knowledge on establishment of danger zone, lack of warning system, lack of proper triage and absence of decontamination plans, lack of special chemical safety outfit and respiratory equipment for rescuers, lack of instructions for proper handling, lack of knowledge in dealing with this type of disaster, and inappropriate evacuation skills and failure to cordon off and insure the location of the incident. Although the initial measures to arrest this crisis was performed based on the health system's instructions of the country with regard to all the possible risks, lack of a comprehensive inter-organizational program and prevention plans, lack of control plans, lack of adequate preparation and response to chemical poisoning, lack of foresight, lack of a risk plan, and lack of an intervention plan for these incidents were the reasons for the damages and problems encountered after the crisis.

Plasmalogens, platelet-activating factor and beyond - Ether lipids in signaling and neurodegeneration

Glycerol-based ether lipids including ether phospholipids form a specialized branch of lipids that in mammals require peroxisomes for their biosynthesis. They are major components of biological membranes and one particular subgroup, the plasmalogens, is widely regarded as a cellular antioxidant. Their vast potential to influence signal transduction pathways is less well known. Here, we summarize the literature showing associations with essential signaling cascades for a wide variety of ether lipids, including platelet-activating factor, alkylglycerols, ether-linked lysophosphatidic acid and plasmalogen-derived polyunsaturated fatty acids. The available experimental evidence demonstrates links to several common players like protein kinase C, peroxisome proliferator-activated receptors or mitogen-activated protein kinases. Furthermore, ether lipid levels have repeatedly been connected to some of the most abundant neurological diseases, particularly Alzheimer's disease and more recently also neurodevelopmental disorders like autism. Thus, we critically discuss the potential role of these compounds in the etiology and pathophysiology of these diseases with an emphasis on signaling processes. Finally, we review the emerging interest in plasmalogens as treatment target in neurological diseases, assessing available data and highlighting future perspectives. Although many aspects of ether lipid involvement in cellular signaling identified in vitro still have to be confirmed in vivo, the compiled data show many intriguing properties and contributions of these lipids to health and disease that will trigger further research.

Hyaluronan and halogen-induced airway hyperresponsiveness and lung injury

Chlorine (Cl2 ) and bromine (Br2 ) are produced in large quantities throughout the world and used in the industry and the sanitation of water. These halogens can pose a significant threat to public health when released into the atmosphere during transportation and industrial accidents, or as acts of terrorism. In this review, we discuss the evidence showing that the activity of Cl2 and Br2 , and of products formed by their interaction with biomolecules, fragment high-molecular-weight hyaluronan (HMW-HA), a key component of the interstitial space and present in epithelial cells, to form proinflammatory, low-molecular-weight hyaluronan fragments that increase intracellular calcium (Ca2+ ) and activate RAS homolog family member A (RhoA) in airway smooth muscle and epithelial and microvascular cells. These changes result in airway hyperresponsiveness (AHR) to methacholine and increase epithelial and microvascular permeability. The increase in intracellular Ca2+ is the result of the activation of the calcium-sensing receptor by Cl2 , Br2 , and their by-products. Posthalogen administration of a commercially available form of HMW-HA to mice and to airway cells in vitro reverses the increase of Ca2+ and the activation of RhoA, and restores AHR to near-normal levels of airway function. These data have established the potential of HMW-HA to be a countermeasure against Cl2 and Br2 toxicity.

Determination of 3-chloro-l-tyrosine as a novel indicator of chlorine poisoning utilizing gas chromatography-mass spectrometric analysis

Chlorine gas exposure occurs in chemical warfare, industrial and household accidents. In forensic science, the generation of chlorine gas by mixing sodium hypochlorite detergent and strong acid detergent cannot be overlooked because of the possibility of suicide method (NaClO + 2HCl → NaCl + H₂O + Cl₂). Though typical autopsy findings are obtained in chlorine exposure, such as pulmonary edema, useful biomarkers don't exist. In this research, we developed an analytical method of 3-chloro-l-tyrosine (Cl-Tyr) in blood as a novel marker of chlorine poisoning utilizing gas chromatography-mass spectrometry (GC-MS). Cl-Tyr was purified using protein precipitation and cation-exchange solid phase extraction, derivatized by the silylation agent and subjected to GC-MS. The quantification range was 10-200 ng/mL and good reproducibility was obtained. We applied the developed method to analyze Cl-Tyr in autopsy sample, which is suspected of chlorine poisoning, and detected 59.7 ng/mL Cl-Tyr in left heart blood. To our knowledge, this is the first report of determination of the chlorinated biomolecule in the human autopsy sample from chlorine poisoning.

Vascular permeability disruption explored in the proteomes of mouse lungs and human microvascular cells following acute bromine exposure

Bromine (Br2) is an organohalide found in nature and is integral to many manufacturing processes. Br2 is toxic to living organisms, and high concentrations can prove fatal. To meet industrial demand, large amounts of purified Br2 are produced, transported, and stored worldwide, providing a multitude of interfaces for potential human exposure through either accidents or terrorism. To identify the key mechanisms associated with acute Br2 exposure, we have surveyed the lung proteomes of C57BL/6 male mice and human lung-derived microvascular endothelial cells (HMECs) at 24 h following exposure to Br2 in concentrations likely to be encountered in the vicinity of industrial accidents. Global discovery proteomics applications combined with systems biology analysis identified robust and highly significant changes in proteins associated with three biological processes: 1) exosome secretion, 2) inflammation, and 3) vascular permeability. We focused on the latter, conducting physiological studies on isolated perfused lungs harvested from mice 24 h after Br2 exposure. These experiments revealed significant increases in the filtration coefficient (Kf) indicating increased permeability of the pulmonary vasculature. Similarly, confluent monolayers of Br2 and Br-lipid-treated HMECs exhibited differential levels of zona occludens-1 that were found to be dissociated from cell wall localization, an increase in phosphorylation and internalization of E-cadherin, as well as increased actin stress fiber formation, all of which are consistent with increased permeability. Taken as a whole, our discovery proteomics and systems analysis workflow, combined with physiological measurements of permeability, revealed both profound and novel biological changes that contribute to our current understanding of Br2 toxicity.

Reactive species generated by heme impair alveolar epithelial sodium channel function in acute respiratory distress syndrome

We previously reported that the highly reactive cell-free heme (CFH) is increased in the plasma of patients with chronic lung injury and causes pulmonary edema in animal model of acute respiratory distress syndrome (ARDS) post inhalation of halogen gas. However, the mechanisms by which CFH causes pulmonary edema are unclear. Herein we report for the first time that CFH and chlorinated lipids (formed by the interaction of halogen gas, Cl₂, with plasmalogens) are increased in the plasma of patients exposed to Cl₂ gas. Ex vivo incubation of red blood cells (RBC) with halogenated lipids caused oxidative damage to RBC cytoskeletal protein spectrin, resulting in hemolysis and release of CFH. Patch clamp and short circuit current measurements revealed that CFH inhibited the activity of amiloride-sensitive epithelial Na⁺ channel (ENaC) and cation sodium (Na⁺) channels in mouse alveolar cells and trans-epithelial Na⁺ transport across human airway cells with EC₅₀ of 125 nM and 500 nM, respectively. Molecular modeling identified 22 putative heme-docking sites on ENaC (energy of binding range: 86-1563 kJ/mol) with at least 2 sites within its narrow transmembrane pore, potentially capable of blocking Na⁺ transport across the channel. A single intramuscular injection of the heme-scavenging protein, hemopexin (4 μg/kg body weight), one hour post halogen gas exposure, decreased plasma CFH and improved lung ENaC activity in mice. In conclusion, results suggested that CFH mediated inhibition of ENaC activity may be responsible for pulmonary edema post inhalation injury.

2-Chlorofatty Aldehyde Elicits Endothelial Cell Activation

Endothelial activation and dysfunction are hallmarks of inflammation. Neutrophil-vascular endothelium interactions have significant effects on vascular wall physiology and pathology. Myeloperoxidase (MPO)-derived products released from activated neutrophils can mediate the inflammatory response and contribute to endothelial dysfunction. 2-Chlorofatty aldehyde (2-ClFALD) is the direct oxidation product of MPO-derived hypochlorous acid (HOCl) targeting plasmalogen phospholipids. The role of 2-ClFALD in endothelial dysfunction is poorly understood and may be dependent on the vascular bed. This study compared the role of 2-ClFALD in eliciting endothelial dysfunction in human coronary artery endothelial cells (HCAEC), human lung microvascular endothelial cells (HLMVEC), and human kidney endothelial cells (HKEC). Profound increases in selectin surface expression as well as ICAM-1 and VCAM-1 surface expression were observed in HCAEC and HLMVEC. The surface expression of these adherence molecules resulted in robust adherence of neutrophils and platelets to 2-ClFALD treated endothelial cells. In contrast to HCAEC and HLMVEC, 2-ClFALD-treated HKEC had substantially reduced adherence molecule surface expression with no resulting increase in platelet adherence. 2-ClFALD-treated HKEC did have an increase in neutrophil adherence. All three endothelial cell lines treated with 2-ClFALD displayed a time-dependent loss of barrier function. Further studies revealed 2-ClHDyA localizes to ER and Golgi when using a synthetic alkyne analog of 2-ClFALD in HCAEC and HLMVEC. These findings indicate 2-ClFALDs promote endothelial cell dysfunction with disparate degrees of responsiveness depending on the vascular bed of origin.

2-Chlorofatty acids are biomarkers of sepsis mortality and mediators of barrier dysfunction in rats

Sepsis is defined as the systemic, dysregulated host immune response to an infection that leads to injury to host organ systems and, often, death. Complex interactions between pathogens and their hosts elicit microcirculatory dysfunction. Neutrophil myeloperoxidase (MPO) is critical for combating pathogens, but MPO-derived hypochlorous acid (HOCl) can react with host molecular species as well. Plasmalogens are targeted by HOCl, leading to the production of 2-chlorofatty acids (2-CLFAs). 2-CLFAs are associated with human sepsis mortality, decrease in vitro endothelial barrier function, and activate human neutrophil extracellular trap formation. Here, we sought to examine 2-CLFAs in an in vivo rat sepsis model. Intraperitoneal cecal slurry sepsis with clinically relevant rescue therapies led to ∼73% mortality and evidence of microcirculatory dysfunction. Plasma concentrations of 2-CLFAs assessed 8 h after sepsis induction were lower in rats that survived sepsis than in nonsurvivors. 2-CLFA levels were elevated in kidney, liver, spleen, lung, colon, and ileum in septic animals. In vivo, exogenous 2-CLFA treatments increased kidney permeability, and in in vitro experiments, 2-CLFA also increased epithelial surface expression of vascular cell adhesion molecule 1 and decreased epithelial barrier function. Collectively, these studies support a role of free 2-CLFAs as biomarkers of sepsis mortality, potentially mediated, in part, by 2-CLFA-elicited endothelial and epithelial barrier dysfunction.

Halogen gas exposure: toxic effects on the parturient

The elemental halogens include chlorine, bromine, and phosgene. Halogen gas can be directly weaponized and employed in warfare or terrorism. Industrial stockpiles or halogen transport can provide targets for terrorist attack as well as an origin for accidental release creating a risk for potential mass-casualty incidents. Pregnant and post-partum women represent a substantial and vulnerable subset of the population who may be at particular risk during an attack or accidental exposure. We review the effects of halogen exposure on the parturient with a focus on bromine toxicity. Bromine is the most extensively studied agent in the context of pregnancy and to-date murine models form the basis for the majority of current knowledge. Pregnancy potentiates the acute lung injury after halogen exposure. In addition, halogen exposure precipitates a preeclamptic-like syndrome in mice. This phenotype is characterized by systemic and pulmonary hypertension, endothelial dysfunction, decreased cardiac output, placental injury and fetal growth restriction. This constellation contributes to increased maternal and fetal mortality observed after bromine exposure. Angiogenic imbalance is noted with overexpression of the soluble fms-like tyrosine kinase-1 (sFlt-1) form of the vascular endothelial growth factor receptor 1 reminiscent of human preeclampsia. Additional research is needed to further explore the effect of halogen gas exposure in pregnancy and to develop therapeutic interventions to mitigate risk to this unique population.

Upregulation of airway smooth muscle calcium-sensing receptor by low-molecular-weight hyaluronan

We investigated the mechanisms involved in the development of airway hyperresponsiveness (AHR) following exposure of mice to halogens. Male mice (C57BL/6; 20-25 g) exposed to either bromine (Br2) or Cl2 (600 or 400 ppm, respectively, for 30 min) developed AHR 24 h after exposure. Nifedipine (5 mg/kg body wt; an L-type calcium channel blocker), administered subcutaneously after Br2 or Cl2 exposure, produced higher AHR compared with Br2 or Cl2 alone. In contrast, diltiazem (5 mg/kg body wt; a nondihydropyridine L-type calcium channel blocker) decreased AHR to control (air) values. Exposure of immortalized human airway smooth muscle cells (hASMC) to Br2 resulted in membrane potential depolarization (Vm Air: 62 ± 3 mV; 3 h post Br2:-45 ± 5 mV; means ± 1 SE; P < 0.001), increased intracellular [Ca2+]i, and increased expression of the calcium-sensing receptor (Ca-SR) protein. Treatment of hASMC with a siRNA against Ca-SR significantly inhibited the Br2 and nifedipine-induced Vm depolarization and [Ca2+]i increase. Intranasal administration of an antagonist to Ca-SR in mice postexposure to Br2 reversed the effects of Br2 and nifedipine on AHR. Incubation of hASMC with low-molecular-weight hyaluronan (LMW-HA), generated by exposing high-molecular-weight hyaluronan (HMW-HA) to Br2, caused Vm depolarization, [Ca2+]i increase, and Ca-SR expression to a similar extent as exposure to Br2 and Cl2. The addition of HMW-HA to cells or mice exposed to Br2, Cl2, or LMW-HA reversed these effects in vitro and improved AHR in vivo. We conclude that detrimental effects of halogen exposure on AHR are mediated via activation of the Ca-SR by LMW-HA.

Vascular Endothelial Growth Factor-121 Administration Mitigates Halogen Inhalation-Induced Pulmonary Injury and Fetal Growth Restriction in Pregnant Mice

Background Circulating levels of sFLT-1 (soluble fms-like tyrosine kinase 1), the extracellular domain of vascular endothelial growth factor (VEGF) receptor 1, and its ratio to levels of placental growth factor are markers of the occurrence and severity of preeclampsia. Methods and Results C57BL/6 pregnant mice on embryonic day 14.5 (E14.5), male, and non-pregnant female mice were exposed to air or to Br2 at 600 ppm for 30 minutes and were treated with vehicle or with VEGF-121 (100 μg/kg, subcutaneously) daily, starting 48 hours post-exposure. Plasma, bronchoalveolar lavage fluid, lungs, fetuses, and placentas were collected 120 hours post-exposure. In Br2-exposed pregnant mice, there was a time-dependent and significant increase in plasma levels of sFLT-1 which correlated with increases in mouse lung wet/dry weights and bronchoalveolar lavage fluid protein content. Supplementation of exogenous VEGF-121 improved survival and weight gain, reduced lung wet/dry weights, decreased bronchoalveolar lavage fluid protein levels, enhanced placental development, and improved fetal growth in pregnant mice exposed to Br2. Exogenous VEGF-121 administration had no effect in non-pregnant mice. Conclusions These results implicate inhibition of VEGF signaling driven by sFLT-1 overexpression as a mechanism of pregnancy-specific injury leading to lung edema, maternal mortality, and fetal growth restriction after bromine gas exposure.

Toxic effects of chlorine gas and potential treatments: a literature review

Chlorine gas is one of the highly produced chemicals in the USA and around the world. Chlorine gas has several uses in water purification, sanitation, and industrial applications; however, it is a toxic inhalation hazard agent. Inhalation of chlorine gas, based on the concentration and duration of the exposure, causes a spectrum of symptoms, including but not limited to lacrimation, rhinorrhea, bronchospasm, cough, dyspnea, acute lung injury, death, and survivors develop signs of pulmonary fibrosis and reactive airway disease. Despite the use of chlorine gas as a chemical warfare agent since World War I and its known potential as an industrial hazard, there is no specific antidote. The resurgence of the use of chlorine gas as a chemical warfare agent in recent years has brought speculation of its use as weapons of mass destruction. Therefore, developing antidotes for chlorine gas-induced lung injuries remains the need of the hour. While some of the pre-clinical studies have made substantial progress in the understanding of chlorine gas-induced pulmonary pathophysiology and identifying potential medical countermeasure(s), yet none of the drug candidates are approved by the U.S. Food and Drug Administration (FDA). In this review, we summarized pathophysiology of chlorine gas-induced pulmonary injuries, pre-clinical animal models, development of a pipeline of potential medical countermeasures under FDA animal rule, and future directions for the development of antidotes for chlorine gas-induced lung injuries.

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 P_aO₂ and an increase in P_aCO₂, 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.

Heme scavenging reduces pulmonary endoplasmic reticulum stress, fibrosis, and emphysema

Pulmonary fibrosis and emphysema are irreversible chronic events after inhalation injury. However, the mechanism(s) involved in their development remain poorly understood. Higher levels of plasma and lung heme have been recorded in acute lung injury associated with several insults. Here, we provide the molecular basis for heme-induced chronic lung injury. We found elevated plasma heme in chronic obstructive pulmonary disease (COPD) (GOLD stage 4) patients and also in a ferret model of COPD secondary to chronic cigarette smoke inhalation. Next, we developed a rodent model of chronic lung injury, where we exposed C57BL/6 mice to the halogen gas, bromine (Br2) (400 ppm, 30 minutes), and returned them to room air resulting in combined airway fibrosis and emphysematous phenotype, as indicated by high collagen deposition in the peribronchial spaces, increased lung hydroxyproline concentrations, and alveolar septal damage. These mice also had elevated pulmonary endoplasmic reticulum (ER) stress as seen in COPD patients; the pharmacological or genetic diminution of ER stress in mice attenuated Br2-induced lung changes. Finally, treating mice with the heme-scavenging protein, hemopexin, reduced plasma heme, ER stress, airway fibrosis, and emphysema. This is the first study to our knowledge to report elevated heme in COPD patients and establishes heme scavenging as a potential therapy after inhalation injury.

Bromine inhalation mimics ischemia-reperfusion cardiomyocyte injury and calpain activation in rats

Halogens are widely used, highly toxic chemicals that pose a potential threat to humans because of their abundance. Halogens such as bromine (Br₂) cause severe pulmonary and systemic injuries; however, the mechanisms of their toxicity are largely unknown. Here, we demonstrated that Br₂ and reactive brominated species produced in the lung and released in blood reach the heart and cause acute cardiac ultrastructural damage and dysfunction in rats. Br₂-induced cardiac damage was demonstrated by acute (3-24 h) increases in circulating troponin I, heart-type fatty acid-binding protein, and NH₂-terminal pro-brain natriuretic peptide. Transmission electron microscopy demonstrated acute (3-24 h) cardiac contraction band necrosis, disruption of z-disks, and mitochondrial swelling and disorganization. Echocardiography and hemodynamic analysis revealed left ventricular (LV) systolic and diastolic dysfunction at 7 days. Plasma and LV tissue had increased levels of brominated fatty acids. 2-Bromohexadecanal (Br-HDA) injected into the LV cavity of a normal rat caused acute LV enlargement with extensive disruption of the sarcomeric architecture and mitochondrial damage. There was extensive infiltration of neutrophils and increased myeloperoxidase levels in the hearts of Br_2- or Br₂ reactant-exposed rats. Increased bromination of sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA) and increased phosphalamban after Br₂ inhalation decreased cardiac SERCA activity by 70%. SERCA inactivation was accompanied by increased Ca²⁺-sensitive LV calpain activity. The calpain-specific inhibitor MDL28170 administered within 1 h after exposure significantly decreased calpain activity and acute mortality. Bromine inhalation and formation of reactive brominated species caused acute cardiac injury and myocardial damage that can lead to heart failure. NEW & NOTEWORTHY The present study defines left ventricular systolic and diastolic dysfunction due to cardiac injury after bromine (Br₂) inhalation. A calpain-dependent mechanism was identified as a potential mediator of cardiac ultrastructure damage. This study not only highlights the importance of monitoring acute cardiac symptoms in victims of Br₂ exposure but also defines calpains as a potential target to treat Br₂-induced toxicity.

Bromofatty aldehyde derived from bromine exposure and myeloperoxidase and eosinophil peroxidase modify GSH and protein

α-Chlorofatty aldehydes (α-ClFALDs) and α-bromofatty aldehydes (α-BrFALDs) are produced in activated neutrophils and eosinophils. This study investigated the ability of α-BrFALD and α-ClFALD to react with the thiols of GSH and protein cysteinyl residues. Initial studies showed that 2-bromohexadecanal (2-BrHDA) and 2-chlorohexadecanal (2-ClHDA) react with GSH producing the same fatty aldehyde-GSH adduct (FALD-GSH). In both synthetic and cellular reactions, FALD-GSH production was more robust with 2-BrHDA compared with 2-ClHDA as precursor. NaBr-supplemented phorbol myristate acetate (PMA)-activated neutrophils formed more α-BrFALD and FALD-GSH compared with non-NaBr-supplemented neutrophils. Primary human eosinophils, which preferentially produce hypobromous acid and α-BrFALD, accumulated FALD-GSH following PMA stimulation. Mice exposed to Br2 gas had increased levels of both α-BrFALD and FALD-GSH in the lungs, as well as elevated systemic plasma levels of FALD-GSH in comparison to mice exposed to air. Similar relative reactivity of α-ClFALD and α-BrFALD with protein thiols was shown using click analogs of these aldehydes. Collectively, these data demonstrate that GSH and protein adduct formation are much greater as a result of nucleophilic attack of cysteinyl residues on α-BrFALD compared with α-ClFALD, which was observed in both primary leukocytes and in mice exposed to bromine gas.

Effects of exposure to water disinfection by-products in a swimming pool: A metabolome-wide association study

BACKGROUND

Exposure to disinfection by-products (DBPs) in drinking water and chlorinated swimming pools are associated with adverse health outcomes, but biological mechanisms remain poorly understood.

OBJECTIVES

Evaluate short-term changes in metabolic profiles in response to DBP exposure while swimming in a chlorinated pool.

MATERIALS AND METHODS

The PISCINA-II study (EXPOsOMICS project) includes 60 volunteers swimming 40min in an indoor pool. Levels of most common DBPs were measured in water and in exhaled breath before and after swimming. Blood samples, collected before and 2h after swimming, were used for metabolic profiling by liquid-chromatography coupled to high-resolution mass-spectrometry. Metabolome-wide association between DBP exposures and each metabolic feature was evaluated using multivariate normal (MVN) models. Sensitivity analyses and compound annotation were conducted.

RESULTS

Exposure levels of all DBPs in exhaled breath were higher after the experiment. A total of 6,471 metabolic features were detected and 293 features were associated with at least one DBP in exhaled breath following Bonferroni correction. A total of 333 metabolic features were associated to at least one DBP measured in water or urine. Uptake of DBPs and physical activity were strongly correlated and mutual adjustment reduced the number of statistically significant associations. From the 293 features, 20 could be identified corresponding to 13 metabolites including compounds in the tryptophan metabolism pathway.

CONCLUSION

Our study identified numerous molecular changes following a swim in a chlorinated pool. While we could not explicitly evaluate which experiment-related factors induced these associations, molecular characterization highlighted metabolic features associated with exposure changes during swimming.

The chlorinated lipidome originating from myeloperoxidase-derived HOCl targeting plasmalogens: Metabolism, clearance, and biological properties

Myeloperoxidase produces the two-electron oxidant HOCl, which targets plasmalogen phospholipids liberating 2-chlorofatty aldehyde. 2-Chlorofatty aldehyde has four known fates: 1) oxidation to 2-chlorofatty acid; 2) reduction to 2-chlorofatty alcohol; 3) Schiff base adduct formation with proteins and amines; and 4) reactivity with glutathione through nucleophilic attack of the α-chlorinated carbon. 2-Chlorofatty acid does not undergo conventional fatty acid β-oxidation due to the presence of the α-chlorinated carbon; however, 2-chlorofatty acid does undergo sequential ω-oxidation and β-oxidation from the ω-end, ultimately resulting in 2-chloroadipic acid urinary excretion. Recent studies have demonstrated that 2-chlorofatty acid clearance is increased by treatment with the PPAR-α agonist WY14643, which increases the enzymatic machinery responsible for hepatic ω-oxidation. Furthermore, 2-chlorofatty acid has been shown to be a PPAR-α agonist, and thus accelerates its own clearance. The roles of 2-chlorofatty aldehyde and 2-chlorofatty acid on leukocyte and endothelial function have been explored by several groups, suggesting that chlorinated lipids induce endothelial cell dysfunction, neutrophil chemotaxis, monocyte apoptosis, and alterations in vascular tone. Thus, the chlorinated lipidome, produced in response to leukocyte activation, is a potential biomarker and therapeutic target to modulate host response in inflammatory diseases.

2-Chlorofatty acids induce Weibel-Palade body mobilization

Endothelial dysfunction is a hallmark of multiple inflammatory diseases. Leukocyte interactions with the endothelium have significant effects on vascular wall biology and pathophysiology. Myeloperoxidase (MPO)-derived oxidant products released from leukocytes are potential mediators of inflammation and endothelial dysfunction. 2-Chlorofatty acids (2-ClFAs) are produced as a result of MPO-derived HOCl targeting plasmalogen phospholipids. Chlorinated lipids have been shown to be associated with multiple inflammatory diseases, but their impact on surrounding endothelial cells has not been examined. This study tested the biological properties of the 2-ClFA molecular species 2-chlorohexadecanoic acid (2-ClHA) on endothelial cells. A synthetic alkyne analog of 2-ClHA, 2-chlorohexadec-15-ynoic acid (2-ClHyA), was used to examine the subcellular localization of 2-ClFA in human coronary artery endothelial cells. Click chemistry experiments revealed that 2-ClHyA localizes to Weibel-Palade bodies. 2-ClHA and 2-ClHyA promote the release of P-selectin, von Willebrand factor, and angiopoietin-2 from endothelial cells. Functionally, 2-ClHA and 2-ClHyA cause neutrophils to adhere to and platelets to aggregate on the endothelium, as well as increase permeability of the endothelial barrier which has been tied to the release of angiopoietin-2. These findings suggest that 2-ClFAs promote endothelial cell dysfunction, which may lead to broad implications in inflammation, thrombosis, and blood vessel stability.

Myeloperoxidase-derived 2-chlorofatty acids contribute to human sepsis mortality via acute respiratory distress syndrome

Sepsis-associated acute respiratory distress syndrome (ARDS) is characterized by neutrophilic inflammation and poor survival. Since neutrophil myeloperoxidase (MPO) activity leads to increased plasma 2-chlorofatty acid (2-ClFA) levels, we hypothesized that plasma concentrations of 2-ClFAs would associate with ARDS and mortality in subjects with sepsis. In sequential consenting patients with sepsis, free 2-ClFA levels were significantly associated with ARDS, and with 30-day mortality, for each log increase in free 2-chlorostearic acid. Plasma MPO was not associated with either ARDS or 30-day mortality but was correlated with 2-ClFA levels. Addition of plasma 2-ClFA levels to the APACHE III score improved prediction for ARDS. Plasma 2-ClFA levels correlated with plasma levels of angiopoietin-2, E selectin, and soluble thrombomodulin. Endothelial cells treated with 2-ClFA responded with increased adhesion molecule surface expression, increased angiopoietin-2 release, and dose-dependent endothelial permeability. Our results suggest that 2-ClFAs derived from neutrophil MPO-catalyzed oxidation contribute to pulmonary endothelial injury and have prognostic utility in sepsis-associated ARDS.

Mechanisms and Treatment of Halogen Inhalation-Induced Pulmonary and Systemic Injuries in Pregnant Mice

Inhalation of oxidant gases has been implicated in adverse outcomes in pregnancy, but animal models to address mechanisms and studies to identify potential pregnancy-specific therapies are lacking. Herein, we show that inhalation of bromine at 600 parts per million for 30 minutes by pregnant mice on the 15th day of embryonic development results in significantly lower survival after 96 hours than an identical level of exposure in nonpregnant mice. On the 19th embryonic day, bromine-exposed pregnant mice have increased systemic blood pressure, abnormal placental development, severe fetal growth restriction, systemic inflammation, increased levels of circulating antiangiogenic short fms-like tyrosine kinase-1, and evidence of pulmonary and cardiac injury. Treatment with tadalafil, an inhibitor of type 5 phosphodiesterase, by oral gavage 1 hour post-exposure and then once daily thereafter, attenuated systemic blood pressures, decreased inflammation, ameliorated pulmonary and cardiac injury, and improved maternal survival (from 36% to 80%) and fetal growth. These pathological changes resemble those seen in preeclampsia. Nonpregnant mice did not exhibit any of these pathological changes and were not affected by tadalafil. These findings suggest that pregnant women exposed to bromine may require particular attention and monitoring for signs of preeclampsia-like symptoms.

Peroxisome proliferator-activated receptor-α accelerates α-chlorofatty acid catabolism

α-Chlorofatty aldehydes are generated from myeloperoxidase-derived HOCl targeting plasmalogens, and are subsequently oxidized to α-chlorofatty acids (α-ClFAs). The catabolic pathway for α-ClFA is initiated by ω-oxidation. Here, we examine PPAR-α activation as a mechanism to increase α-ClFA catabolism. Pretreating both HepG2 cells and primary mouse hepatocytes with the PPAR-α agonist, pirinixic acid (Wy 14643), increased the production of α-chlorodicarboxylic acids (α-ClDCAs) in cells treated with exogenous α-ClFA. Additionally, α-ClDCA production in Wy 14643-pretreated wild-type mouse hepatocytes was accompanied by a reduction in cellular free α-ClFA. The dependence of PPAR-α-accelerated α-ClFA catabolism was further demonstrated by both impaired metabolism in mouse PPAR-α^-/- hepatocytes and decreased clearance of plasma α-ClFA in PPAR-α^-/- mice. Furthermore, Wy 14643 treatments decreased plasma 2-chlorohexadecanoic acid levels in wild-type mice. Additional studies showed that α-ClFA increases PPAR-α, PPAR-δ, and PPAR-γ activities, as well as mRNA expression of the PPAR-α target genes, CD36, CPT1a, Cyp4a10, and CIDEC. Collectively, these results indicate that PPAR-α accelerates important pathways for the clearance of α-ClFA, and α-ClFA may, in part, accelerate its catabolism by serving as a ligand for PPAR-α.

l-α-Phosphatidylglycerol Chlorohydrins as Potential Biomarkers for Chlorine Gas Exposure

Chlorine is a widely available toxic chemical that has been repeatedly used in armed conflict globally. The Organization for the Prohibition of Chemical Weapons (OPCW) have on numerous occasions found "compelling confirmation" that chlorine gas has been used against civilians in northern Syria. However, currently, there are no analytical methods available to unambiguously prove chlorine gas exposure. In this study, we describe the screening for chlorinated biomolecules by the use of mass isotope ratio filters followed by the identification of two biomarkers present in bronchoalveolar lavage fluid (BALF) from chlorine gas exposed mice. The relevance of these markers for human exposure was verified by their presence in in vitro chlorinated human BALF. The biomarkers were detectable for 72 h after exposure and were absent in nonexposed control animals. Furthermore, the biomarkers were not detected in humans diagnosed with chronic respiratory diseases. The potential chlorine specific markers were all chlorohydrins of unsaturated pulmonary surfactant phospholipids; phosphatidylglycerols, and phosphatidylcholines. Mass spectrometry fragmentation characteristics were favorable for the phosphatidylglycerol chlorohydrins, and they were therefore proposed as the best biomarker candidates.