A Novel Topical Ophthalmic Formulation to Mitigate Acute Mustard Gas Keratopathy In Vivo: A Pilot Study

Washing with buffered vitamin C after corrosive chemical (sodium hypochlorite) exposure reduces ocular depth of injury

Chemical eye injuries occur in home, industrial, and military settings. The standard recommended treatment after exposure of the eyes to chemical toxins is washing with tap water for at least 15 min. An estimated 80 % of ocular toxins are associated with reactive oxygen species and/or extreme pH. Using food-source eyes and a commercially available test kit for depth of injury (IVD EITTM) that measures the depth of dead corneal keratocytes by fragmented DNA staining, washing the eye with a buffered vitamin C solution significantly reduced corneal keratocyte cell death and depth of injury compared to control. When eyes were washed (using a 500-mL eyewash bottle) for 15 min with water after exposure to 32 % sodium hypochlorite (chlorine bleach), the depth of injury was 59.6 ± 3.6 %, a level of damage predicted to cause extreme/permanent eye injury or even blindness in vivo (extreme or irreversible injury, GHS category 1), but washing with 0.2 % buffered vitamin C after bleach exposure reduced damage to13.8 ± 1.4 %, which is significantly less (P < 0.001) and predicted by the IVD EIT method to be reversible irritation (GHS category 2) that will heal within 21 days in vivo.

PI3K signaling and lysyl oxidase is critical to corneal stroma fibrosis following mustard gas injury

Sulfur mustard gas (SM), an alkylating and vesicating agent, has been used frequently in many wars and conflicts. SM exposure to the eye results in several corneal abnormalities including scar/fibrosis formation. However, molecular mechanism for SM induced corneal fibrosis development is poorly understood. After SM insult to the eye, excessive synthesis/secretion of extracellular matrix components (ECM) including collagen (COL) I, COL III, and lysyl oxidase (LOX) by corneal myofibroblasts causes corneal fibrosis, however, precise mechanism remains elusive. This study tested the hypothesis that Phosphoinositide 3-kinase (PI3K) signaling alterations post SM in cornea enhances stromal ECM synthesis and corneal fibrosis. New Zealand White Rabbits were used. The right eyes were exposed to SM (200 mg-min/m3) and left eye to the air for 8min at MRI Global. Rabbit corneas were collected on day-3, day-7, and day-14 for molecular analysis. SM exposure caused a significant increase in mRNA expression of PI3K, AKT, COL I, COL III, and LOX and protein levels of LOX in a time-dependent manner in rabbit corneas. The in vitro studies were performed with human corneal stromal fibroblasts (hCSFs) by growing cultures in -/+ nitrogen mustard (NM) and LY294002, a PI3K specific inhibitor, for 30min, 8h, 24h, 48h, and 72h. NM significantly increased mRNA and protein levels of PI3K, AKT, COL I, COL III, and LOX. On the contrary, LY294002 in NM hCSFs significantly reduced PI3K, AKT, COL I, COL III, and LOX protein expression. We concluded that PI3K signaling mediates stromal collagen synthesis and LOX production following SM injury.

Mustard Gas Induced Corneal Injury Involves Ferroptosis and p38 MAPK Signaling

Purpose

Sulfur mustard gas (SM) exposure to eyes causes multiple corneal injuries including stromal cell loss in vivo. However, mechanisms mediating stromal cell loss/death remains elusive. This study sought to test the novel hypothesis that SM-induced toxicity to human corneal stromal fibroblasts involves ferroptosis mechanism via p38 MAPK signaling.

Methods

New Zealand white rabbit corneas, naïve and SM exposed (200 mg-min/m3 for eight minutes and collected after three days) were used to examine the levels of cell death and reactive oxygen species (ROS) for in vivo studies. Donor human corneas were used to generate primary human corneal stromal fibroblasts (hCSF) for in vitro studies. The hCSFs were exposed to nitrogen mustard (NM; SM analogue) at various timepoints (30 minutes, eight hours, and 24 hours). A p38 MAPK specific inhibitor, SB202190, was also used. Quantitative reverse transcription polymerase chain reaction, Western blotting, reactive oxygen species (ROS), lipid peroxidation, live/dead assay, and RNASeq were used in various investigations.

Results

SM caused a significant increase in cell death and ROS production three days after SM exposure in rabbit corneas. NM exposure to hCSF demonstrated a significant increase in ROS, lipid peroxidation, and ferroptosis biomarkers ACSL4 (inducer) and significant decrease in reducer (SLC7A11 and GPX4) compared to controls in a time-dependent manner. The inhibition of p38 MAPK promoted cell survival and reduced ROS production following mustard gas exposure.

Conclusions

The results of in vivo and in vitro investigations uncovered a novel mechanism that mustard gas toxicity to the cornea involves ferroptosis pathway and p38 MAPK activation.

Dexamethasone sodium phosphate loaded nanoparticles for prevention of nitrogen mustard induced corneal injury

Nitrogen mustard (NM) is a potent vesicating chemical warfare agent that is primarily absorbed through skin, inhalation, or ocular surface. Ocular exposure of NM can cause acute to chronic keratopathy which can eventually lead to blindness. There is a current lack of effective countermeasures against ocular exposure of NM despite their imperative need. Herein, we aim to explore the sustained effect of Dexamethasone sodium phosphate (DSP)-loaded polymeric nanoparticles (PLGA-DSP-NP) following a single subconjunctival injection in the management and prevention of corneal injury progression upon exposure to NM. DSP is an FDA approved corticosteroid with proven anti-inflammatory properties. We formulated PLGA-DSP-NP with zinc chelation ion bridging method using PLGA polymer, with particles of approximately 250 nm and a drug loading of 6.5 wt%. Under in vitro sink conditions, PLGA-DSP-NP exhibited a sustained drug release for two weeks. Notably, in NM injured cornea, a single subconjunctival (SCT) injection of PLGA-DSP-NP outperformed DSP eyedrops (0.1%), DSP solution, placebo NP, and saline, significantly mitigating corneal neovascularization, ulceration, and opacity for the two weeks study period. Through PLGA-DSP-NP injection, sustained DSP release hindered inflammatory cytokine recruitment, angiogenic factors, and endothelial cell proliferation in the cornea. This strategy presents a promising localized corticosteroid delivery system to effectively combat NM-induced corneal injury, offering insights into managing vesicant exposure.

Chloropicrin induced ocular injury: Biomarkers, potential mechanisms, and treatments

Ocular tissue, especially the cornea, is overly sensitive to chemical exposures. The availability and adoption of chemical threat agent chloropicrin (CP) is growing in the United States as a pesticide and fumigant; thereby increasing the risk of its use in warfare, terrorist attacks and non-intentional exposure. Exposure to CP results in immediate ocular, respiratory, and dermal injury; however, we lack knowledge on its mechanism of toxicity as well as of its breakdown products like chlorine and phosgene, and effective therapies are elusive. Herein, we have reviewed the recent findings on exposure route, toxicity and likely mechanisms of CP induced ocular toxicity based on other vesicating chemical warfare agents that cause ocular injury. We have focused on the implication of their toxicity and mechanistic outcomes in the ocular tissue, especially the cornea, which could be useful in the development of broad-spectrum effective therapeutic options. We have discussed on the potential countermeasures, overall hallmarks and challenges involved in studying ocular injuries from chemical threat agent exposures. Finally, we reviewed useful available technologies and methods that can assist in the identification of effective medical countermeasures for chemical threat agents related ocular injuries.

Tissue-targeted and localized AAV5-DCN and AAV5-PEDF combination gene therapy abrogates corneal fibrosis and concurrent neovascularization in rabbit eyes in vivo

PURPOSE

Corneal fibrosis and neovascularization (CNV) after ocular trauma impairs vision. This study tested therapeutic potential of tissue-targeted adeno-associated virus5 (AAV5) mediated decorin (DCN) and pigment epithelium-derived factor (PEDF) combination genes in vivo.

METHODS

Corneal fibrosis and CNV were induced in New Zealand White rabbits via chemical trauma. Gene therapy in stroma was delivered 30-min after chemical-trauma via topical AAV5-DCN and AAV5-PEDF application using a cloning cylinder. Clinical eye examinations and multimodal imaging in live rabbits were performed periodically and corneal tissues were collected 9-day and 15-day post euthanasia. Histological, cellular, and molecular and apoptosis assays were used for efficacy, tolerability, and mechanistic studies.

RESULTS

The AAV5-DCN and AAV5-PEDF combination gene therapy significantly reduced corneal fibrosis (p < 0.01 or p < 0.001) and CNV (p < 0.001) in therapy-given (chemical-trauma and AAV5-DCN + AAV5-PEDF) rabbit eyes compared to the no-therapy given eyes (chemical-trauma and AAV5-naked vector). Histopathological analyses demonstrated significantly reduced fibrotic α-smooth muscle actin and endothelial lectin expression in therapy-given corneas compared to no-therapy corneas on day-9 (p < 0.001) and day-15 (p < 0.001). Further, therapy-given corneas showed significantly increased Fas-ligand mRNA levels (p < 0.001) and apoptotic cell death in neovessels (p < 0.001) compared to no-therapy corneas. AAV5 delivered 2.69 × 107 copies of DCN and 2.31 × 107 copies of PEDF genes per μg of DNA. AAV5 vector and delivered DCN and PEDF genes found tolerable to the rabbit eyes and caused no significant toxicity to the cornea.

CONCLUSION

The combination AAV5-DCN and AAV5-PEDF topical gene therapy effectively reduces corneal fibrosis and CNV with high tolerability in vivo in rabbits. Additional studies are warranted.

Differential gene expression and protein-protein interaction network profiling of sulfur mustard-exposed rabbit corneas employing RNA-seq data and bioinformatics tools

Sulfur mustard (SM) ocular exposure severely damages the cornea and causes vision impairment. At present, no specific therapy exists to mitigate SM-induced corneal injury and vision loss. This study performed transcriptome profiling of naïve, SM-damaged, and SM-undamaged rabbit corneas using RNA-seq analysis and bioinformatic tools to gain a better mechanistic understanding and develop SM-specific medical countermeasures. The mRNA profiles of rabbit corneas 4 weeks post SM vapor exposure were generated using Illumina-NextSeq deep sequencing (Gene Expression Omnibus accession # GSE127708). The RNA sequences of naïve (n = 4), SM-damaged (n = 5), and SM-undamaged (n = 5) corneas were subjected to differential expression (DE) analysis after quality control profiling with FastQC. DE analysis was performed using HISAT2, StringTie, and DESeq2. The log2(FC)±2 and adjusted p˂0.05 were chosen to identify the most relevant genes. A total of 5930 differentially expressed genes (DEGs) (upregulated: 3196, downregulated: 2734) were found in SM-damaged corneas compared to naïve corneas, whereas SM-undamaged corneas showed 1884 DEGs (upregulated: 1029, downregulated: 855) compared to naïve corneas. DE profiling of SM-damaged corneas to SM-undamaged corneas revealed 985 genes (upregulated: 308, downregulated: 677). The DE profiles were subsequently subjected to signaling pathway enrichment, and protein‒protein interactions (PPIs) were analyzed. Pathway enrichment was performed for the genes associated with cellular apoptosis, death, adhesion, migration, differentiation, proliferation, extracellular matrix, and tumor necrosis factor production. To identify novel targets, we narrowed the pathway analysis to upregulated and downregulated genes associated with cell proliferation and differentiation, and PPI networks were developed. Furthermore, protein targets associated with cell differentiation and proliferation that may play vital roles in corneal fibrosis and wound healing post SM injury were identified.

Mustard Gas Exposure Actuates SMAD2/3 Signaling to Promote Myofibroblast Generation in the Cornea

Sulfur mustard gas (SM) is a vesicating and alkylating agent used as a chemical weapon in many mass-casualty incidents since World War I. Ocular injuries were reported in >90% of exposed victims. The mechanisms underlying SM-induced blindness remain elusive. This study tested the hypothesis that SM-induced corneal fibrosis occurs due to the generation of myofibroblasts from resident fibroblasts via the SMAD2/3 signaling pathway in rabbit eyes in vivo and primary human corneal fibroblasts (hCSFs) isolated from donor corneas in vitro. Fifty-four New Zealand White Rabbits were divided into three groups (Naïve, Vehicle, SM-Vapor treated). The SM-Vapor group was exposed to SM at 200 mg-min/m3 for 8 min at the MRI Global facility. Rabbit corneas were collected on day 3, day 7, and day 14 for immunohistochemistry, RNA, and protein lysates. SM caused a significant increase in SMAD2/3, pSMAD, and ɑSMA expression on day 3, day 7, and day 14 in rabbit corneas. For mechanistic studies, hCSFs were treated with nitrogen mustard (NM) or NM + SIS3 (SMAD3-specific inhibitor) and collected at 30 m, 8 h, 24 h, 48 h, and 72 h. NM significantly increased TGFβ, pSMAD3, and SMAD2/3 levels. On the contrary, inhibition of SMAD2/3 signaling by SIS3 treatment significantly reduced SMAD2/3, pSMAD3, and ɑSMA expression in hCSFs. We conclude that SMAD2/3 signaling appears to play a vital role in myofibroblast formation in the cornea following mustard gas exposure.

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.

Carbofuran pesticide toxicity to the eye

Pesticide exposure to eyes is a major source of ocular morbidities in adults and children all over the world. Carbofuran (CF), N-methyl carbamate, pesticide is most widely used as an insecticide, nematicide, and acaricide in agriculture, forestry, and gardening. Contact or ingestion of carbofuran causes high morbidity and mortality in humans and pets. Pesticides are absorbed in the eye faster than other organs of the body and damage ocular tissues very quickly. Carbofuran exposure to eye causes blurred vision, pain, loss of coordination, anti-cholinesterase activities, weakness, sweating, nausea and vomiting, abdominal pain, endocrine, reproductive, and cytotoxic effects in humans depending on amount and duration of exposure. Pesticide exposure to eye injures cornea, conjunctiva, lens, retina, and optic nerve and leads to abnormal ocular movement and vision impairment. Additionally, anticholinesterase pesticides like carbofuran are known to cause salivation, lacrimation, urination, and defecation (SLUD). Carbofuran and its two major metabolites (3-hydroxycarbofuran and 3-ketocarbofuran) are reversible inhibitors of acetylcholinesterase (AChE) which regulates acetylcholine (ACh), a neurohumoral chemical that plays an important role in corneal wound healing. The corneal epithelium contains high levels of ACh whose accumulation by AChE inhibition after CF exposure overstimulates muscarinic ACh receptors (mAChRs) and nicotinic ACh receptors (nAChRs). Hyper stimulation of mAChRs in the eye causes miosis (excessive constriction of the pupil), dacryorrhea (excessive flow of tears), or chromodacryorrhea (red tears). Recent studies reported alteration of autophagy mechanism in human cornea in vitro and ex vivo post carbofuran exposure. This review describes carbofuran toxicity to the eye with special emphasis on corneal morbidities and blindness.

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.

Corneal stromal repair and regeneration

The cornea is a specialized, transparent, avascular, immune-privileged, and heavily innervated tissue that affords 2/3rd of refraction to the eye. Ocular injuries, infections, and genetic factors affect corneal function and cause vision impairment. Presently, a variety of laser/non-laser surgeries, immunosuppressants, and/or corneal transplants are predominantly used to revive sight in human patients. The development of novel, precision-guided, and tissue-targeted non-surgical therapies promoting corneal repair and regeneration based on mechanistic understanding is of paramount importance to reduce the impact of global blindness. Research over the past decade revealed that modulation of pathological signaling pathways and factors by a variety of therapeutic delivery methods effectively treats corneal disorders including corneal scar/haze, inflammation, and angiogenesis in various pre-clinical animal models and are primed for human translation. This review discusses recent advances in the areas of corneal repair, restoration, and regeneration. Herein, we provide an overview of evolving approaches and therapeutic modalities that have shown great promise in reviving corneal transparency and function through the use of small drug molecules, gene therapy, nanomedicine, stem cells, trophic factors, exosomes, stromal equivalents, bioengineered stromal scaffolds, tissue adhesives, and 3D bioprinting.

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.

Research models of sulfur mustard- and nitrogen mustard-induced ocular injuries and potential therapeutics

Sulfur mustard (SM) is a notorious, bifunctional alkylating vesicant that was first used in warfare during World War I in 1917 and since then has been deployed in numerous skirmishes with its most recent documented use being during the Middle Eastern conflicts. Apart from its use in combat and terrorist activities, continual threat of accidental exposure from old stockpiles and improperly discarded munitions is ever present, especially to the innocent and unassuming civilian populations. SM can cause devastating injuries, depending on the dosage of SM exposure, route of exposure, as well as the physiological conditions of the individuals exposed. The most common routes of exposure are ocular, dermal, and exposure to the lungs and respiratory tissues through inhalation. Eyes are the most susceptible organ to SM-induced toxicities owing to their high moisture content and rapidly dividing cells. Additionally, ocular injury causes the most expeditious disablement of individuals even upon whole-body exposures. Therefore, it is imperative to understand the mechanisms underlying SM-induced ocular toxicity and design therapeutic interventions to prevent/mitigate ocular injuries. Ocular SM exposure may cause a wide range of symptoms such as inflammation, lacrimation, itching, dryness, photophobia, edema of the cornea/sclera/retina/iris, conjunctivitis, degradation of the corneal layer, fusion of two or more ocular layers, neovascularization, fibrosis, and temporary or permanent structural damage to one or more ocular layers. These symptoms may lead to vision impairments, resulting in partial or complete blindness that may be permanent. The highly toxic and exceedingly notorious nature of SM makes it a highly regulated chemical, requiring very expensive licensing, security, and safety requirements; thus, the more easily accessible analogue, nitrogen mustard (NM) that mimics SM-induced toxicity and injuries is employed in plethora of studies conducted in different animal models and culture systems. This review provides a comprehensive account of the injuries and symptoms that occur upon ocular SM exposures in human patients as well as studies in animal (in vivo, ex vivo) and cell (in vitro) models of SM and NM ocular exposures. Special emphasis has been laid on highlighting the strengths and lacunae in the research as well as the possible unexplored avenues of mechanisms underlying mustard-induced ocular injury that can be explored in future research endeavors. Furthermore, development of therapeutic interventions and targets of interest in the ocular system exposed to SM and NM, based on studies in human patients as well as in vivo, ex vivo, and in vitro models has been discussed in great depth, providing a valuable knowledge database to delineate pathways associated with vesicant-induced toxicity, and strategies/diagnostic tools against SM-induced toxicity.

Effects of Regular/Dilute Proparacaine Anesthetic Eye Drops in Combination with Ophthalmic Antibiotics on Corneal Wound Healing

Purpose: Topical, local anesthetic eye drops in conjunction with antibiotics are commonly used to reduce ocular pain and treat patients in emergency clinics; however, their effects on corneal healing are poorly understood. This study examined whether regular or diluted proparacaine eye drops given in combination with common ophthalmic antibiotics affect corneal wound healing parameters using in vitro and in vivo models. Methods: Primary human corneal fibroblasts generated from donor corneas and New Zealand white rabbits were used. Regular (0.5%) and diluted (0.05%) proparacaine eye drops, twice daily for 3 days, were applied to cultures and rabbit eyes, with or without ophthalmic antibiotics (polymyxin B sulfate and trimethoprim). Trypan blue, 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT), and scratch wound assays measured cellular viability, proliferation, and migration, respectively, in vitro. Slit lamp biomicroscopy, tonometry, fluorescein eye test, hematoxylin and eosin (H&E) staining, and 4',6-diamidino-2-phenylindole (DAPI) immunofluorescence were used for in vivo studies. Results: Both regular and diluted proparacaine affected wound healing response in the cornea in vitro and in vivo in a time-dependent manner. Adjunct antibiotic treatments had additive effects characterized by reduced corneal fibroblast viability, proliferation, and migration in vitro and corneal epithelial recovery in vivo. Regular proparacaine with antibiotics showed most pronounced effects on corneal wound healing parameters, and diluted proparacaine without antibiotics had minimal negative effects in vitro and in vivo. Conclusions: Both methods of regular (0.5%) and diluted (0.05%) proparacaine topical application to the cornea are safe, but impede corneal wound healing in vitro and in vivo. Adjunct antibiotic treatments had additive negative effects on corneal wound repair.

Autophagy in Extracellular Matrix and Wound Healing Modulation in the Cornea

Autophagy is a robust cellular mechanism for disposing of harmful molecules or recycling them to cells, which also regulates physiopathological processes in cornea. Dysregulated autophagy causes inefficient clearance of unwanted proteins and cellular debris, mitochondrial disorganization, defective inflammation, organ dysfunctions, cell death, and diseases. The cornea accounts for two-thirds of the refraction of light that occurs in the eyes, but is prone to trauma/injury and infection. The extracellular matrix (ECM) is a noncellular dynamic macromolecular network in corneal tissues comprised of collagens, proteoglycans, elastin, fibronectin, laminins, hyaluronan, and glycoproteins. The ECM undergoes remodeling by matrix-degrading enzymes and maintains corneal transparency. Autophagy plays an important role in the ECM and wound healing maintenance. Delayed/dysregulated autophagy impacts the ECM and wound healing, and can lead to corneal dysfunction. Stromal wound healing involves responses from the corneal epithelium, basement membrane, keratocytes, the ECM, and many cytokines and chemokines, including transforming growth factor beta-1 and platelet-derived growth factor. Mild corneal injuries self-repair, but greater injuries lead to corneal haze/scars/fibrosis and vision loss due to disruptions in the ECM, autophagy, and normal wound healing processes. Presently, the precise role of autophagy and ECM remodeling in corneal wound healing is elusive. This review discusses recent trends in autophagy and ECM modulation in the context of corneal wound healing and homeostasis.

Ocular toxicity of mustard gas: A concise review

Sulfur mustard (SM) is a chemical warfare agent that has been used throughout recent history and remains a threat today. Exposed soldiers and civilians experience a variety of symptoms primarily in the respiratory system, skin, and eyes. The ocular tissues are highly sensitive to damage by SM and undergo unique manifestations of acute, chronic, and delayed complications that can persist for months and years after exposure. The mechanisms of this unique mustard gas keratopathy are still not fully understood and animal models for the study of this disease are discussed. Recent advances in mechanisms of injury are included in this review. Ophthalmic manifestations of SM injury including persistent epithelial defects, limbal stem cell deficiency, corneal neovascularization, dry eye, and corneal opacification have been reported. A wide variety of medical and surgical therapies have been studied and are reviewed here along with potential future therapies.

Dose-dependent emergence of acute and recurrent corneal lesions in sulfur mustard-exposed rabbit eyes

Sulfur mustard (SM) is a lipid soluble alkylating agent that causes genotoxic injury. The eye is highly sensitive to SM toxicity and exposures exceeding 400 mg min/m³ can elicit irreversible corneal pathophysiologies. Development of medical countermeasures for ocular SM exposure has been hindered by a limited understanding of dose-dependent effects of SM on corneal injury. Here, clinical, histological and ultrastructural analyses were used to characterize the effects of SM dose on corneal injury progression. Corneas were evaluated for up to 20 wk following exposure to saturated SM vapor for 30-150 s, which corresponds to 300-1,500 mg min/m³. In acute studies, a ceiling effect on corneal edema developed at doses associated with full-thickness corneal lesions, implicating endothelial toxicity in corneal swelling. Recurrent edematous lesions (RELs) transiently emerged after 2 wk in a dose-dependent fashion, followed by the development of secondary corneal pathophysiologies such as neovascularization, stromal scarring and endothelial abnormalities. RELs appeared in 96 % of corneas exposed for ≥ 90 s, 52 % of corneas exposed for 60 s and 0 % of corneas exposed for 30 s. While REL latency was variable in corneas exposed for 60 s, REL emergence was synchronized at exposures ≥ 90 s. Corneas did not exhibit more than one REL, suggesting RELs are part of a programmed pathophysiological response to severe alkylating lesions. In post-mortem studies at 12 wk, corneal edema was positively correlated to severity of endothelial pathologies, consistent with previous findings that endothelial toxicity influences long-term outcomes. These results provide novel insight into long-term corneal pathophysiological responses to acute toxicity and identify exposure conditions suitable for therapeutic testing.

The Need for Improved Therapeutic Approaches to Protect the Cornea Against Chemotoxic Injuries

Cornea, a highly specialized transparent tissue, is the major refractive element of the eye. The cornea is highly susceptible to chemotoxic injury through topical exposure to vapors, microparticles, and aqueous drops, as well as through systemically absorbed chemicals that access the cornea via tear film, aqueous humor, and limbal vasculature. Corneal injury activates a carefully orchestrated series of repair processes capable of resolving minor lesions over time, but it often fails to overcome the menace of moderate, severe, and chronic injuries and secondary pathophysiologies that permanently impair vision. The most serious complications of chemical injuries-persistent corneal edema, neovascularization, scarring/haze, limbal stem cell deficiency, and corneal melting-often manifest over months to years, suggesting that a better understanding of endogenous regenerative mechanisms of corneal repair can lead to the development of improved treatments that may attenuate or prevent corneal defects and protect vision.