A rabbit model for evaluating ocular damage from acrolein toxicity in vivo

Research progress on animal models of corneal epithelial-stromal injury

A corneal epithelial-stromal defect is recognized as a major contributor to corneal scarring. Given the rising prevalence of blindness caused by corneal scarring, increasing attention has been focused on corneal epithelial-stromal defects. Currently, the etiology and pathogenesis of these defects remain inadequately understood, necessitating further investigation through experimental research. Various modeling methods exist both domestically and internationally, each with distinct adaptive conditions, advantages, and disadvantages. This review primarily aims to summarize the techniques used to establish optimal animal models of corneal epithelial-stromal injury, including mechanical modeling, chemical alkali burns, post-refractive surgery infections, and genetic engineering. The intention is to provide valuable insights for studying the mechanisms underlying corneal epithelial-stromal injury and the development of corresponding therapeutic interventions.

Toxicological effects of ocular acrolein exposure to eyelids in rabbits in vivo

Acrolein is a highly reactive volatile toxic chemical that injures the eyes and many organs. It has been used in wars and terrorism for wounding masses on multiple occasions and is readily accessible commercially. Our earlier studies revealed acrolein's toxicity to the cornea and witnessed damage to other ocular tissues. Eyelids play a vital role in keeping eyes mobile, moist, lubricated, and functional utilizing a range of diverse lipids produced by the Meibomian glands located in the upper and lower eyelids. This study sought to investigate acrolein's toxicity to eyelid tissues by studying the expression of inflammatory and lipid markers in rabbit eyes in vivo utilizing our reported vapor-cap model. The study was approved by the institutional animal care and use committees and followed ARVO guidelines. Twelve New Zealand White Rabbits were divided into 3 groups: Naïve (group 1), 1-min acrolein exposure (group 2), or 3-min acrolein exposure (group 3). The toxicological effects of acrolein on ocular health in live animals were monitored with regular clinical eye exams and intraocular pressure measurements and eyelid tissues post-euthanasia were subjected to H&E and Masson's trichrome histology and qRT-PCR analysis. Clinical eye examinations witnessed severely swollen eyelids, abnormal ocular discharge, chemosis, and elevated intraocular pressure (p < 0.001) in acrolein-exposed eyes. Histological studies supported clinical findings and exhibited noticeable changes in eyelid tissue morphology. Gene expression studies exhibited significantly increased expression of inflammatory and lipid mediators (LOX, PAF, Cox-2, and LTB4; p < 0.001) in acrolein-exposed eyelid tissues compared to naïve eyelid tissues. The results suggest that acrolein exposure to the eyes causes acute damage to eyelids by altering inflammatory and lipid mediators in vivo.

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.

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.

Corneal fibrosis abrogation by a localized AAV-mediated inhibitor of differentiation 3 (Id3) gene therapy in rabbit eyes in vivo

Previously we found that inhibitor of differentiation 3 (Id3) gene, a transcriptional repressor, efficiently inhibits corneal keratocyte differentiation to myofibroblasts in vitro. This study evaluated the potential of adeno-associated virus 5 (AAV5)-mediated Id3 gene therapy to treat corneal scarring using an established rabbit in vivo disease model. Corneal scarring/fibrosis in rabbit eyes was induced by alkali trauma, and 24 h thereafter corneas were administered with either balanced salt solution AAV5-naked vector, or AAV5-Id3 vector (n = 6/group) via an optimized reported method. Therapeutic effects of AAV5-Id3 gene therapy on corneal pathology and ocular health were evaluated with clinical, histological, and molecular techniques. Localized AAV5-Id3 gene therapy significantly inhibited corneal fibrosis/haze clinically from 2.7 to 0.7 on the Fantes scale in live animals (AAV5-naked versus AAV5-Id3; p < 0.001). Furthermore, AAV5-Id3 treatment significantly reduced profibrotic gene mRNA levels: α-smooth muscle actin (α-SMA) (2.8-fold; p < 0.001), fibronectin (3.2-fold; p < 0.001), collagen I (0.8-fold; p < 0.001), and collagen III (1.4-fold; p < 0.001), as well as protein levels of α-SMA (23.8%; p < 0.001) and collagens (1.8-fold; p < 0.001). The anti-fibrotic activity of AAV5-Id3 is attributed to reduced myofibroblast formation by disrupting the binding of E-box proteins to the promoter of α-SMA, a transforming growth factor-β signaling downstream target gene. In conclusion, these results indicate that localized AAV5-Id3 delivery in stroma caused no clinically relevant ocular symptoms or corneal cellular toxicity in the rabbit eyes.

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.

The Adverse Effects of Air Pollution on the Eye: A Review

Air pollution is inevitably the result of human civilization, industrialization, and globalization. It is composed of a mixture of gases and particles at harmful levels. Particulate matter (PM), nitrogen oxides (NOx), and carbon dioxides (CO₂) are mainly generated from vehicle emissions and fuel consumption and are the main materials causing outdoor air pollution. Exposure to polluted outdoor air has been proven to be harmful to human eyes. On the other hand, indoor air pollution from environmental tobacco smoking, heating, cooking, or poor indoor ventilation is also related to several eye diseases, including conjunctivitis, glaucoma, cataracts, and age-related macular degeneration (AMD). In the past 30 years, no updated review has provided an overview of the impact of air pollution on the eye. We reviewed reports on air pollution and eye diseases in the last three decades in the PubMed database, Medline databases, and Google Scholar and discussed the effect of various outdoor and indoor pollutants on human eyes.

Long-Term Safety and Tolerability of BMP7 and HGF Gene Overexpression in Rabbit Cornea

Purpose

Tissue-targeted localized BMP7+HGF genes delivered into the stroma via nanoparticle effectively treats corneal fibrosis and rehabilitates transparency in vivo without acute toxicity. This study evaluated the long-term safety and tolerability of BMP7+HGF nanomedicine for the eye in vivo.

Methods

One eye each of 36 rabbits received balanced salt solution (group 1, naïve; n = 12), naked vector with polyethylenimine-conjugated gold nanoparticles (PEI2-GNP; group 2, naked-vector; n = 12), or BMP7+HGF genes with PEI2-GNP (group 3, BMP7+HGF; n = 12) via a topical delivery technique. Safety and tolerability measurements were performed by clinical biomicroscopy in live rabbits at predetermined time intervals up to 7 months. Corneal tissues were collected at 2 months and 7 months after treatment and subjected to histology, immunofluorescence, and quantitative real-time PCR analyses.

Results

Clinical ophthalmic examinations and modified MacDonald-Shadduck scores showed no significant changes in corneal thickness (P = 0.3389), tear flow (P = 0.2121), intraocular pressure (P = 0.9958), epithelial abrasion, or ocular abnormality. Slit-lamp, stereo, confocal, and specular biomicroscopy showed no signs of blepharospasm chemosis, erythema, epiphora, abnormal ocular discharge, or changes in epithelium, stroma, and endothelium after BMP7+HGF therapy for up to 7 months, as compared with control groups. Throughout the 7-month period, no significant changes were recorded in endothelial density (P = 0.9581). Histological and molecular data were well corroborated with the subjective clinical analyses and showed no differences in the naïve, naked-vector, and BMP7+HGF groups.

Conclusions

Localized BMP7+HGF therapy is a safe, tolerable, and innovative modality for the treatment of corneal fibrosis.

Translational Relevance

Nanoparticle-mediated BMP7+HGF combination gene therapy has the potential to treat corneal fibrosis in vivo without short- or long-term toxicity.

Glutathione is a potential therapeutic target for acrolein toxicity in the cornea

Toxic and volatile chemicals are widely used in household products and previously used as warfare agents, causing a public health threat worldwide. This study aimed to evaluate the extent of injury and mechanisms of acrolein toxicity in the cornea. Primary human corneal stromal fibroblasts cultures (hCSFs) from human donor cornea were cultured and exposed to acrolein toxicity with -/+ N-acetylcysteine (NAC) to study the mode of action in the presence of Buthionine sulphoximine (BSO). PrestoBlue and MTT assays were used to optimize acrolein, NAC, and BSO doses for hCSFs. Cell-based assays and qRT-PCR analyses were performed to understand the acrolein toxicity and mechanisms. Acrolein exposure leads to an increased reactive oxygen species (ROS), compromised glutathione (GSH) levels, and mitochondrial dysfunction. The TUNEL and caspase assays showed that acrolein caused cell death in hCSFs. These deleterious effects can be mitigated using NAC in hCSFs, suggesting that GSH can be a potential target for acrolein toxicity in the cornea.