Therapeutic measures for sulfur mustard-induced ocular injury

Mechanisms of Apoptosis and Pulmonary Fibrosis Resulting From Sulfur Mustard-Induced Acute Pulmonary Injury in Rats

Sulfur mustard (SM) is a highly toxic bifunctional alkylating agent that inflicts severe damage on the respiratory tract. Although numerous studies have examined the mechanisms underlying SM-induced pulmonary injury, the exact pathways involved remain unclear. This study aims to investigate an acute pulmonary injury model, with SM administered as a single intraperitoneal injection (8 mg/kg) or single intratracheal instillation (2 mg/kg) at equal toxicity doses (1LD50). The results revealed that epithelial cells in the alveolar septa of the intraperitoneal SM group exhibited a significantly higher expression of apoptotic markers, including pro-apoptotic protein Bax, caspase-3, and caspase-9 proteins, than those in the tracheal SM group. Conversely, the expression of the anti-apoptotic protein Bcl-2 was significantly lower in the intraperitoneal SM group than in the tracheal SM group, as confirmed by TUNEL staining and immunohistochemical staining. The intraperitoneal SM group exhibited markedly higher expression of fibrosis-related proteins, including MMP-2, MMP-9, TIMP-1, TIMP-2, collagen type I, collagen type III, TGF-β1, and Smad7, than the tracheal SM group. These markers, detected through immunohistochemical immunolabeling, indicate a more significant fibrotic response in the intraperitoneal group. In summary, this study demonstrates that intraperitoneal exposure to SM results in increased apoptosis, elevated expression of pro-apoptotic proteins, and fibrosis-related proteins in the alveolar epithelial cells compared with intratracheal exposure, even at equivalent toxicity levels. Our findings highlight the suitability of the intraperitoneal route for further investigation and identify apoptotic and fibrosis-related proteins as potential targets for intervention in SM-induced pulmonary injury.

Mouse Model of Nitrogen Mustard Ocular Surface Injury Characterization and Sphingolipid Signaling

Vesicating chemicals like sulfur mustard (SM) or nitrogen mustard (NM) can cause devastating damage to the eyes, skin, and lungs. Eyes, being the most sensitive, have complicated pathologies that can manifest immediately after exposure (acute) and last for years (chronic). No FDA-approved drug is available to be used as medical counter measures (MCMs) against such injuries. Understanding the pathological mechanisms in acute and chronic response of the eye is essential for developing effective MCMs. Here, we report the clinical and histopathological characterization of a mouse model of NM-induced ocular surface injury (entire surface) developed by treating the eye with 2% (w/v) NM solution for 5 min. Unlike the existing models of specific injury, our model showed severe ocular inflammation, including the eyelids, structural deformity of the corneal epithelium and stroma, and diminished visual and retinal functions. We also observed alterations of the inflammatory markers and their expression at different phases of the injury, along with an activation of acidic sphingomyelinase (aSMase), causing an increase in bioactive sphingolipid ceramide and a reduction in sphingomyelin levels. This novel ocular surface mouse model recapitulated the injuries reported in human, rabbit, and murine SM or NM injury models. NM exposure of the entire ocular surface in mice, which is similar to accidental or deliberate exposure in humans, showed severe ocular inflammation and caused irreversible alterations to the corneal structure and significant vision loss. It also showed an intricate interplay between inflammatory markers over the injury period and alteration in sphingolipid homeostasis in the early acute phase.

Oxidative stress reactions in rats with pulmonary injuries induced by sulfur mustard (1 LD50)

OBJECTIVE

Sulfur mustard (SM) is an important chemical warfare agent. The mechanisms underlying SM toxicity have not been completely elucidated. However, oxidative stress and the subsequent damage to macromolecules have been considered ascrucial steps in SM toxicity. In this study, a rat model of SM-induced acute pulmonary injury was established using an equal toxicity dose (1LD50). This study employed two methods to directly compare oxidative stress indices in serum enzymes and the epithelial cells of the alveolar septa.

METHODS

Male Sprague-Dawley rats were randomly divided into intraperitoneal SM, intraperitoneal propylene glycol control, tracheal SM, tracheal propylene glycol control, and control groups. SM-induced serum enzyme levels and protein expression in the epithelial cells of the alveolar septa were measured using enzyme-linked immunosorbent assay and immunohistochemistry.

RESULTS

Serum levels of superoxide dismutase, catalase, and glutathione peroxidase were upregulated in the intraperitoneal SM group compared with those in the tracheal SM group. Positive expression ratios of CuZn-superoxide dismutase, Mn-superoxide dismutase, paraoxonase-1, and apolipoprotein-1 proteins in the epithelial cells of the alveolar septa in the intraperitoneal SM group were elevated compared with those in the tracheal SM group.

CONCLUSION

Under SM (1LD50) exposure, there were significantly higher serum enzyme levels and protein expressions in the epithelial cells of the alveolar septa of rats injected with SM intraperitoneally compared with SM administered by intratracheal instillation. The results demonstrated that the differences in oxidative stress indices at the molecular level in SM-induced pulmonary injury were dependent on the route of exposure.

Predicting clinical outcome of sulfur mustard induced ocular injury using machine learning model

The sight-threatening sulfur mustard (SM) induced ocular injury presents specific symptoms in each clinical stage. The acute injury develops in all exposed eyes and may heal or deteriorate into chronic late pathology. Early detection of eyes at risk of developing late pathology may assist in providing unique monitoring and specific treatments only to relevant cases. In this study, we evaluated a machine-learning (ML) model for predicting the development of SM-induced late pathology based on clinical data of the acute phase in the rabbit model. Clinical data from 166 rabbit eyes exposed to SM vapor was used retrospectively. The data included a comprehensive clinical evaluation of the cornea, eyelids and conjunctiva using a semi-quantitative clinical score. A random forest classifier ML model, was trained to predict the development of corneal neovascularization four weeks post-ocular exposure to SM vapor using clinical scores recorded three weeks earlier. The overall accuracy in predicting the clinical outcome of SM-induced ocular injury was 73%. The accuracy in identifying eyes at risk of developing corneal neovascularization and future healed eyes was 75% and 59%, respectively. The most important parameters for accurate prediction were conjunctival secretion and corneal opacity at 1w and corneal erosions at 72 h post-exposure. Predicting the clinical outcome of SM-induced ocular injury based on the acute injury parameters using ML is demonstrated for the first time. Although the prediction accuracy was limited, probably due to the small dataset, it pointed out towards various parameters during the acute injury that are important for predicting SM-induced late pathology and revealing possible pathological mechanisms.

The Use of Hydrogel Dressings in Sulfur Mustard-Induced Skin and Ocular Wound Management

Over one century after its first military use on the battlefield, sulfur mustard (SM) remains a threatening agent. Due to the absence of an antidote and specific treatment, the management of SM-induced lesions, particularly on the skin and eyes, still represents a challenge. Current therapeutic management is mainly limited to symptomatic and supportive care, pain relief, and prevention of infectious complications. New strategies are needed to accelerate healing and optimize the repair of the function and appearance of damaged tissues. Hydrogels have been shown to be suitable for healing severe burn wounds. Because the same gravity of lesions is observed in SM victims, hydrogels could be relevant dressings to improve wound healing of SM-induced skin and ocular injuries. In this article, we review how hydrogel dressings may be beneficial for improving the wound healing of SM-induced injuries, with special emphasis placed on their suitability as drug delivery devices on SM-induced skin and ocular lesions.

Mustard Gas-Induced Ocular Surface Disorders: An Update on the Pathogenesis, Clinical Manifestations, and Management

PURPOSE

Mustard gas (MG) is a potent blistering and alkylating agent that has been used for military and terrorism purposes. Ocular surface injuries are common after exposure to MG. This review provides an update on the pathophysiology, ocular surface complications, and treatment options for MG-related ocular injuries.

METHODS

Required information was obtained by reviewing various databases such as Cochrane Library, Google Scholar, and PubMed until March 2022. Data were collected by using keywords: "mustard gas" OR "sulfur mustard" AND "eye" OR "cornea" OR "ocular complication" OR "keratitis" OR "keratopathy" OR "limbal stem cell deficiency" OR "dry eye."

RESULTS

Chronic intracellular toxicity, inflammation, and ischemia have been shown to play an essential role in the pathogenesis of MG injury. Ocular surface injuries can have acute, chronic, and most distinctly a delayed-onset presentation leading to various degrees of limbal stem cell deficiency. To date, no treatment has been agreed on as the standard treatment for chronic/delayed-onset MG keratopathy. Based on the authors' experience, we propose a management algorithm for MG-related ocular surface injuries involving optimization of ocular health, anti-inflammatory therapy, and if needed surgical interventions. The management of chronic and delayed-onset presentation remains challenging.

CONCLUSIONS

MG keratopathy is a unique form of chemical injury which can lead to a range of ocular surface pathologies. Long-term anti-inflammatory therapy even in patients with seemingly mild disease may potentially reduce the likelihood of the development of more severe delayed-onset disease.

Progress towards a standardized model of ocular sulfur mustard injury for therapeutic testing

Sulfur mustard (SM) remains a highly dangerous chemical weapon capable of producing mass casualties through liquid or vapor exposure. The cornea is highly sensitive to SM toxicity and exposure to low vapor doses can cause incapacitating acute injuries. At higher doses, corneas fail to fully heal and subsequently develop a constellation of symptoms known as mustard gas keratopathy (MGK) that causes reduced quality of life and impaired or lost vision. Despite a century of research, there are no specific treatments for acute or persistent ocular SM injuries. Here I summarize toxicological, clinical and pathophysiological mechanisms of SM vapor injury in the cornea, describe a preclinical model of ocular SM vapor exposure for reproducible therapeutic studies, and propose new approaches to improve evaluation of therapeutic effects. I also describe recent findings illustrating the delayed development of a transient but severe recurrent corneal lesion that, in turn, triggers the emergence of secondary keratopathies characteristic of the chronic form of MGK. Development of this recurrent lesion is SM dose-dependent, although the severity of the recurrent lesion appears SM dose-independent. Similar recurrent lesions have been reported in multiple species, including humans. Given the mechanistic relationship between the recurrent lesion and chronic, secondary keratopathies, I hypothesize that preventing the development of the recurrent lesion represents a novel and potentially valuable therapeutic approach for treatment of severe corneal SM injuries. Although ocular exposure to SM vapor continues to be a challenging therapeutic target, establishing consistent and reproducible models of corneal injury that enhance mechanistic and pathophysiological understanding will help satisfy regulatory requirements and accelerate the development of effective therapies.

The use of aflibercept (VEGF trap) in mitigating sulfur mustard-induced corneal neovascularization in a rabbit model

Sulfur mustard (SM)-induced ocular injury is characterized by an acute inflammatory response that may become chronic or enter a latent phase with delayed pathology. This study aimed to evaluate the efficacy of ziv-aflibercept and aflibercept in preventing and ameliorating corneal neovascularization (NV), respectively, following chemical eye exposure to SM vapor in a rabbit model. Chemical SM ocular insult was induced in the right eye of rabbits. A single application of ziv-aflibercept was administered 2 h or 9 days post-exposure. A single subconjunctival aflibercept treatment in an ocular formulation was administered 4 weeks after SM vapor exposure and subsequent to an initial 1-week treatment with 0.1 % dexamethasone. Clinical monitoring was performed 5-12 weeks post-exposure, and digital corneal pictures were taken to assess the extent of NV. The rabbits were euthanized and the corneas were processed for histological assessment. Treatment with ziv-aflibercept 2 h and 9 days post-exposure moderately reduced insult severity and partially delayed or prevented corneal NV. Aflibercept application 4 weeks post-exposure significantly reduced the extent of NV for 8 weeks. The substantial decrease in existing corneal NV in this group was confirmed by histology. These results reveal the powerful anti-angiogenic efficacy of the VEGF-trap for ameliorating existing NV as opposed to preventing NV development, revealing the ability of this treatment to mitigate corneal NV.

Time-dependent in situ structural and cellular aberrations in rabbit cornea in vivo after mustard gas exposure

An array of corneal pathologies collectively called mustard gas keratopathy (MGK) resulting from ocular exposure to sulfur mustard (SM) gas are the most prevalent chemical warfare injury. MGK involves chronic ocular discomfort that results in vision impairment. The etiology of MGK remains unclear and poorly understood primarily due to a lack of scientific data regarding structural and cellular changes in different layers of the cornea altered by mustard vapor exposure in vivo. The goals of this study were to (a) characterize time-dependent changes in different layers of corneal epithelium, stroma, and endothelium in live animals in situ by employing state-of-the-art multimodal clinical ophthalmic imaging techniques and (b) determine if SM-induced acute changes in corneal cells could be rescued by a topical eye drop (TED) treatment using in an established rabbit in vivo model. Forty-five New Zealand White Rabbit eyes were divided into four groups (Naïve, TED, SM, and SM + TED). Only one eye was exposed to SM (200 mg-min/m3 for 8 min), and each group had three time points with six eyes each (Table-1). TED was topically applied twice a day for seven days. Clinical eye examinations and imaging were performed in live rabbits with stereo, Slit-lamp, HRT-RCM3, and Spectralis microscopy system. Fantes grading, fluorescein staining, Schirmer's tests, and applanation tonometry were conducted to measure corneal haze, ocular surface aberrations, tears, and intraocular pressure respectively. H&E and PSR staining were used for histopathological cellular changes in the cornea. In vivo confocal and OCT imaging revealed significant changes in structural and morphological appearance of corneal epithelium, stroma, and endothelium in vivo in SM-exposed rabbit corneas in a time-dependent manner compared to naïve cornea. Also, SM-exposed eyes showed loss of corneal transparency characterized by increased stromal thickness and light-scattering myofibroblasts or activated keratocytes, representing haze formation in the cornea. Neither naive nor TED-alone treated eyes showed any structural, cellular, and functional abnormalities. Topical TED treatment significantly reduced SM-induced abnormalities in primary corneal layers. We conclude that structural and cellular changes in primary corneal layers are early pathological events contributing to MGK in vivo, and efficient targeting of them with suitable agents has the potential to mitigate SM ocular injury.

Sulfur mustard corneal injury is associated with alterations in the epithelial basement membrane and stromal extracellular matrix

Sulfur mustard (SM; bis(2-chloroethyl) sulfide) is a highly reactive bifunctional alkylating agent synthesized for chemical warfare. The eyes are particularly sensitive to SM where it causes irritation, pain, photophobia, and blepharitis, depending on the dose and duration of exposure. In these studies, we examined the effects of SM vapor on the corneas of New Zealand white male rabbits. Edema and hazing of the cornea, signs of acute injury, were observed within one day of exposure to SM, followed by neovascularization, a sign of chronic or late phase pathology, which persisted for at least 28 days. Significant epithelial-stromal separation ranging from ~8-17% of the epithelial surface was observed. In the stroma, there was a marked increase in CD45+ leukocytes and a decrease of keratocytes, along with areas of disorganization of collagen fibers. SM also disrupted the corneal basement membrane and altered the expression of perlecan, a heparan sulfate proteoglycan, and cellular fibronectin, an extracellular matrix glycoprotein. This was associated with an increase in basement membrane matrix metalloproteinases including ADAM17, which is important in remodeling of the basement membrane during wound healing. Tenascin-C, an extracellular matrix glycoprotein, was also upregulated in the stroma 14-28 d post SM, a finding consistent with its role in organizing structural components of the stroma necessary for corneal transparency. These data demonstrate that SM vapor causes persistent alterations in structural components of the cornea. Further characterization of SM-induced injury in rabbit cornea will be useful for the identification of targets for the development of ocular countermeasures.

Pathophysiology and inflammatory biomarkers of sulfur mustard-induced corneal injury in rabbits

Sulfur mustard (SM) is a cytotoxic, vesicating, chemical warfare agent, first used in 1917; corneas are particularly vulnerable to SM exposure. They may develop inflammation, ulceration, neovascularization (NV), impaired vision, and partial/complete blindness depending upon the concentration of SM, exposure duration, and bio-physiological conditions of the eyes. Comprehensive in vivo studies have established ocular structural alterations, opacity, NV, and inflammation upon short durations (<4 min) of SM exposure. In this study, detailed analyses of histopathological alterations in corneal structure, keratocytes, inflammatory cells, blood vessels, and expressions of cyclooxygenase (COX)-2, matrix metalloproteinase (MMP)-9, vascular endothelial growth factor (VEGF), and cytokines were performed in New Zealand white rabbits, in a time-dependent manner till 28 days, post longer durations (5 and 7 min) of ocular SM exposure to establish quantifiable endpoints of injury and healing. Results indicated that SM exposure led to duration-dependent increases in corneal thickness, opacity, ulceration, epithelial-stromal separation, and epithelial degradation. Significant increases in NV, keratocyte death, blood vessels, and inflammatory markers (COX-2, MMP-9, VEGF, and interleukin-8) were also observed for both exposure durations compared to the controls. Collectively, these findings would benefit in temporal delineation of mechanisms underlying SM-induced corneal toxicity and provide models for testing therapeutic interventions.

Advice on assistance and protection provided by the Scientific Advisory Board of the Organisation for the Prohibition of Chemical Weapons: Part 3. On medical care and treatment of injuries from sulfur mustard

Blister agents damage the skin, eyes, mucous membranes and subcutaneous tissues. Other toxic effects may occur after absorption. The response of the Scientific Advisory Board (SAB) of the Organisation for the Prohibition of Chemical Weapons (OPCW) to a request from the OPCW Director-General in 2013 on the status of medical countermeasures and treatments to blister agents is updated through the incorporation of the latest information. The physical and toxicological properties of sulfur mustard and clinical effects and treatments are summarised. The information should assist medics and emergency responders who may be unfamiliar with the toxidrome of sulfur mustard and its treatment.