Corneal organ culture model for assessing epithelial responses to surfactants

Gelatin-Chitosan Hydrogel Biological, Antimicrobial and Mechanical Properties for Dental Applications

Chitosan, a natural polysaccharide sourced from crustaceans and insects, is often used with hydrogels in wound care. Evaluating its cytotoxicity and antimicrobial properties is crucial for its potential use in dentistry.

OBJECTIVE

To investigate the mechanical properties of gelatin hydrogels based on decaethylated chitosan and antimicrobial activity against Streptococcus mutans and their biological effects with stem cells from apical papilla (SCAPs).

MATERIAL AND METHODS

Gelatin-chitosan hydrogels were synthesized at concentrations of 0%, 0.2% and 0.5%. Enzymatic and hydrolytic degradation, along with swelling capacity, was assessed. Fourier transform infrared spectroscopy (FTIR) analysis was employed to characterize the hydrogels. The interaction between hydrogels and SCAPs was examined through initial adhesion and cell proliferation at 24 and 48 h, using the Thiazolyl Blue Tetrazolium Bromide (MTT assay). The antimicrobial effect was evaluated using agar diffusion and a microdilution test against S. mutans. Uniaxial tensile strength (UTS) was also measured to assess the mechanical properties of the hydrogels.

RESULTS

The hydrogels underwent hydrolytic and enzymatic degradation at 30, 220, 300 min and 15, 25, 30 min, respectively. Significantly, (p < 0.01) swelling capacity occurred at 20, 40, 30 min, respectively. Gelatin-chitosan hydrogels' functional groups were confirmed using vibrational pattern analysis. SCAPs proliferation corresponded to 24 h = 73 ± 2%, 82 ± 2%, 61 ± 6% and 48 h = 83 ± 11%, 86 ± 2%, 44 ± 2%, respectively. The bacterial survival of hydrogel interaction was found to be 96 ± 1%, 17 ± 1.5% (p < 0.01) and 1 ± 0.5% (p < 0.01), respectively. UTS showed enhanced (p < 0.05) mechanical properties with chitosan presence.

CONCLUSION

Gelatin-chitosan hydrogels displayed favorable degradation, swelling capacity, mild dose-dependent cytotoxicity, significant proliferation with stem cells from apical papilla (SCAPs), substantial antimicrobial effects against S. mutans and enhanced mechanical properties. These findings highlight their potential applications as postoperative care dressings.

Eyedrop-based macromolecular ophthalmic drug delivery for ocular fundus disease treatment

Therapeutic antibodies are extensively used to treat fundus diseases by intravitreal injection, as eyedrop formulation has been rather challenging due to the presence of ocular barriers. Here, an innovative penetrating carrier was developed for antibody delivery in eyedrop formulations. We found that fluorocarbon-modified chitosan (FCS) would self-assemble with proteins to form nanocomplexes, which could effectively pass across the complicated ocular structure to reach the posterior eye segments in both mice and rabbits. In a choroidal melanoma-bearing mouse model, eyedrops containing FCS/anti-PDL1 could induce stronger antitumor immune responses than those triggered by intravenous injection of anti-PDL1. Moreover, in choroidal neovascularization-bearing mouse and rabbit models, FCS/anti-VEGFA eyedrops effectively inhibited vascular proliferation, achieving comparable therapeutic responses to those observed with intravitreal injection of anti-VEGFA. Our work presents an effective delivery carrier to treat fundus diseases using eyedrop of therapeutic proteins, which may enable at-home treatment of many eye diseases with great patient compliance.

3D cell culture model: From ground experiment to microgravity study

Microgravity has been shown to induce many changes in cell growth and differentiation due to offloading the gravitational strain normally exerted on cells. Although many studies have used two-dimensional (2D) cell culture systems to investigate the effects of microgravity on cell growth, three-dimensional (3D) culture scaffolds can offer more direct indications of the modified cell response to microgravity-related dysregulations compared to 2D culture methods. Thus, knowledge of 3D cell culture is essential for better understanding the in vivo tissue function and physiological response under microgravity conditions. This review discusses the advances in 2D and 3D cell culture studies, particularly emphasizing the role of hydrogels, which can provide cells with a mimic in vivo environment to collect a more natural response. We also summarized recent studies about cell growth and differentiation under real microgravity or simulated microgravity conditions using ground-based equipment. Finally, we anticipate that hydrogel-based 3D culture models will play an essential role in constructing organoids, discovering the causes of microgravity-dependent molecular and cellular changes, improving space tissue regeneration, and developing innovative therapeutic strategies. Future research into the 3D culture in microgravity conditions could lead to valuable therapeutic applications in health and pharmaceuticals.

Synthetic Extracellular Matrices for 3D Culture of Schwann Cells, Hepatocytes, and HUVECs

Synthetic hydrogels from polyisocyanides (PIC) are a type of novel thermoreversible biomaterials, which can covalently bind biomolecules such as adhesion peptides to provide a suitable extracellular matrix (ECM)-like microenvironment for different cells. Although we have demonstrated that PIC is suitable for three-dimensional (3D) culture of several cell types, it is unknown whether this hydrogel sustains the proliferation and passaging of cells originating from different germ layers. In the present study, we propose a 3D culture system for three representative cell sources: Schwann cells (ectoderm), hepatocytes (endoderm), and endothelial cells (mesoderm). Both Schwann cells and hepatocytes proliferated into multicellular spheroids and maintained their properties, regardless of the amount of cell-adhesive RGD motifs in long-term culture. Notably, Schwann cells grew into larger spheroids in RGD-free PIC than in PIC-RGD, while HL-7702 showed the opposite behavior. Endothelial cells (human umbilical vein endothelial cells, HUVECs) spread and formed an endothelial cell (EC) network only in PIC-RGD. Moreover, in a hepatocyte/HUVEC co-culture system, the characteristics of both cells were well kept for a long period in PIC-RGD. In all, our work highlights a simple ECM mimic that supports the growth and phenotype maintenance of cells from all germ layers in the long term. Our findings might contribute to research on biological development, organoid engineering, and in vitro drug screening.

Enhanced topical corticosteroids delivery to the eye: A trade-off in strategy choice

Topical corticosteroids are the primary treatment of ocular inflammation caused by surgery, injury, or other conditions. Drug pre-corneal residence time, drug water solubility, and drug corneal permeability coefficient are the major factors that determine the ocular drug bioavailability after topical administration. Although growing research successfully enhanced local delivery of corticosteroids utilizing various strategies, rational and dynamic approaches to strategy selection are still lacking. Within this review, an overview of the various strategies as well as their performance in retention, solubility, and permeability coefficient of corticosteroids are provided. On this basis, the tradeoff of strategy selection is discussed, which may shed light on the rational choice and application of ophthalmic delivery enhancement strategies.

Establishment of a Robust and Simple Corneal Organ Culture Model to Monitor Wound Healing

The use of in vitro systems to investigate the process of corneal wound healing offers the opportunity to reduce animal pain inflicted during in vivo experimentation. This study aimed to establish an easy-to-handle ex vivo organ culture model with porcine corneas for the evaluation and modulation of epithelial wound healing. Cultured free-floating cornea disks with a punch defect were observed by stereomicroscopic photo documentation. We analysed the effects of different cell culture media and investigated the impact of different wound sizes as well as the role of the limbus. Modulation of the wound healing process was carried out with the cytostatic agent Mitomycin C. The wound area calculation revealed that after three days over 90% of the lesion was healed. As analysed with TUNEL and lactate dehydrogenase assay, the culture conditions were cell protecting and preserved the viability of the corneal tissue. Wound healing rates differ dependent on the culture medium used. Mitomycin C hampered wound healing in a concentration-dependent manner. The porcine cornea ex vivo culture ideally mimics the in vivo situation and allows investigations of cellular behaviour in the course of wound healing. The effect of substances can be studied, as we have documented for a mitosis inhibitor. This model might aid in toxicological studies as well as in the evaluation of drug efficacy and could offer a platform for therapeutic approaches based on regenerative medicine.

Clearance of Gram-Negative Bacterial Pathogens from the Ocular Surface by Predatory Bacteria

It was previously demonstrated that predatory bacteria are able to efficiently eliminate Gram-negative pathogens including antibiotic-resistant and biofilm-associated bacteria. In this proof-of-concept study we evaluated whether two species of predatory bacteria, Bdellovibrio bacteriovorus and Micavibrio aeruginosavorus, were able to alter the survival of Gram-negative pathogens on the ocular surface. Clinical keratitis isolates of Pseudomonas aeruginosa (strain PAC) and Serratia marcescens (strain K904) were applied to the ocular surface of NZW rabbits followed by application of predatory bacteria. At time intervals, surviving pathogenic bacteria were enumerated. In addition, B. bacteriovorus and S. marcescens were applied to porcine organ culture corneas under contact lenses, and the ocular surface was examined by scanning electron microscopy. The ocular surface epithelial layer of porcine corneas exposed to S. marcescens, but not B. bacteriovorus was damaged. Using this model, neither pathogen could survive on the rabbit ocular surface for longer than 24 h. M. aeruginosavorus correlated with a more rapid clearance of P. aeruginosa but not S. marcescens from rabbit eyes. This study supports previous evidence that predatory bacteria are well tolerated by the cornea, but suggest that predatory bacteria do not considerably change the ability of the ocular surface to clear the tested Gram-negative bacterial pathogens from the ocular surface.

Applications of Biomaterials in 3D Cell Culture and Contributions of 3D Cell Culture to Drug Development and Basic Biomedical Research

The process of evaluating the efficacy and toxicity of drugs is important in the production of new drugs to treat diseases. Testing in humans is the most accurate method, but there are technical and ethical limitations. To overcome these limitations, various models have been developed in which responses to various external stimuli can be observed to help guide future trials. In particular, three-dimensional (3D) cell culture has a great advantage in simulating the physical and biological functions of tissues in the human body. This article reviews the biomaterials currently used to improve cellular functions in 3D culture and the contributions of 3D culture to cancer research, stem cell culture and drug and toxicity screening.

Neuronal hyperexcitability and astrocyte activation in spinal dorsal horn of a dermatitis mouse model with cutaneous hypersensitivity

Cleaning products such as soaps, shampoos, and detergents are comprised mainly of surfactants, agents known to cause dermatitis and cutaneous hypersensitivity characterized by itching, stinging, and burning of the skin and scalp. However, the mechanisms underlying surfactant-induced cutaneous hypersensitivity remain unclear. In the present study, we investigated the mechanisms of cutaneous hypersensitivity in mice treated with the detergent sodium dodecyl sulfate (SDS). Repeated SDS application to the skin induced inflammation, xeroderma, and elongation of peripheral nerves into the epidermis. The number of neurons immunopositive for c-Fos, a well known marker of neural activity, was substantially higher (+441%) in spinal dorsal horn (SDH) lamina I-II (but not lamina III-VI) of SDS-treated mice compared to vehicle-treated mice. In vivo extracellular recording revealed enhanced spontaneous (+64%) and non-noxious mechanical stimulation-evoked firing (+139%) of SDH lamina I-II neurons in SDS-treated mice, and stimulation-evoked neuronal firing was sustained (+5333%) even after stimulation. The number of GFAP-positive (activated) astrocytes, but not Iba1-positive microglia, was also elevated (+137%) in SDH lamina I-II of SDS-treated mice compared to vehicle-treated mice. Peripheral nerve elongation and hyperexcitability of afferent or SDH neurons, possible associated with the activation of spinal astrocytes, may underlie cutaneous hypersensitivity induced by surfactants.

Safety assessment of antibiotic administration by magnetic nanoparticles in in vitro zebrafish liver and intestine cultures

Different in vitro models have been suggested to replace in vivo studies. In vitro studies are of great interest and give the opportunity to analyze cellular responses in a closed system with stable experimental conditions and to avoid direct animal exposure and distress during the experiments. These methods are useful to test drugs and chemicals toxicity in order to better understand their environmental impact. In the present study, fish organ cultures have been used to test different oxytetracycline exposure methods, including oxide nanoparticles (IONPs), using zebrafish as experimental model. Results showed that oxytetracycline accumulation at the end of the experiment (24 h) in the exposed organs did not show any significant difference in the analyzed samples and was not dependent on the exposure way (free or IONPs-bound oxytetracycline). However, as regards molecular analysis, the different exposure ways tested in this study showed some differences in the expression of genes involved in stress response. The present data did not completely agree with a previous in vivo study performed in zebrafish using IONPs, underlying that replacement of in vivo models with in vitro studies cannot always represent the complexity of interactions typical of a biological system.

Inappropriate modeling of chronic and complex disorders: How to reconsider the approach in the context of predictive, preventive and personalized medicine, and translational medicine

Preclinical investigations such as animal modeling make the basis of clinical investigations and subsequently patient care. Predictive, preventive, and personalized medicine (PPPM) not only highlights a patient-tailored approach by choosing the right medication, the right dose at the right time point but it as well essentially requires early identification, by the means of complex and state-of-the-art technologies of unmanifested pathological processes in an individual, in order to deliver targeted prevention early enough to reverse manifestation of a pathology. Such an approach can be achieved by taking into account clinical, pathological, environmental, and psychosocial characteristics of the patients or an individual who has a suboptimal health condition. Inappropriate modeling of chronic and complex disorders, in this context, may diminish the predictive potential and slow down the development of PPPM and consequently modern healthcare. Therefore, it is the common goal of PPPM and translational medicine to find the solution for the problem we present in our review. Both, translational medicine and PPPM in parallel, essentially need accurate surrogates for misleading animal models. This study was therefore undertaken to provide shreds of evidence against the validity of animal models. Limitations of current animal models and drug development strategies based on animal modeling have been systematically discussed. Finally, a variety of potential surrogates have been suggested to change the unfavorable situation in medical research and consequently in healthcare.

Development and Assessment of a Novel Canine Ex Vivo Corneal Model

PURPOSE

To develop a novel ex vivo extended culture model of canine corneal epithelial cell wound healing.

MATERIALS AND METHODS

Canine corneoscleral rims (CSR) were obtained and, after preparation for culture, were placed on a nutating scaffold and incubated in physiological conditions. In experiment 1, eight CSR in a serum-containing antimicrobial-fortified medium were monitored for epithelial integrity and bacterial infection up to 28 days in culture. CSR were assessed histologically at the end of the culture period end points 0, 7, 14, and 28 days with accompanying scanning electron microscopic (SEM) and transmission electron microscopic (TEM) evaluation. Samples for microbial culture were obtained at days 0, 3, 7, 14, and 28. In experiment 2, uniform 8-mm-diameter superficial corneal epithelial wounds were created and monitored for re-epithelialization in the same culture conditions or in a serum-free protein equivalent medium, with four CSR per group. Standardized digital images were obtained with cobalt filter at the time of fluorescein staining and media change every six hours. Image J imaging software was used to measure the area of fluorescein retention. Re-epithelialization rates were calculated and CSR then fixed for immunohistochemistry (IHC).

RESULTS

All corneas survived to end points as described in experiment 1 with no evidence of contamination or compromised epithelial integrity. Histologically, a multilayered epithelium was maintained and corneal edema was not appreciated until day 14. SEM examination revealed epithelial cell layer confluence and migrating epithelial cells of normal cellular morphology with normal cell-cell interactions on TEM. In experiment 2, all eight corneas healed with a healing rate of 0.702 ± 0.130 mm²/h (1.25 mm/day epithelial cell migration rate) and were positive in IHC evaluation for markers of corneal fibrosis.

CONCLUSION

This ex vivo canine corneal wound healing model is an appropriate and clinically relevant tool for assessment and modulation of epithelial wound healing.

The use of in vivo, ex vivo, in vitro, computational models and volunteer studies in vision research and therapy, and their contribution to the Three Rs

Much is known about mammalian vision, and considerable progress has been achieved in treating many vision disorders, especially those due to changes in the eye, by using various therapeutic methods, including stem cell and gene therapy. While cells and tissues from the main parts of the eye and the visual cortex (VC) can be maintained in culture, and many computer models exist, the current non-animal approaches are severely limiting in the study of visual perception and retinotopic imaging. Some of the early studies with cats and non-human primates (NHPs) are controversial for animal welfare reasons and are of questionable clinical relevance, particularly with respect to the treatment of amblyopia. More recently, the UK Home Office records have shown that attention is now more focused on rodents, especially the mouse. This is likely to be due to the perceived need for genetically-altered animals, rather than to knowledge of the similarities and differences of vision in cats, NHPs and rodents, and the fact that the same techniques can be used for all of the species. We discuss the advantages and limitations of animal and non-animal methods for vision research, and assess their relative contributions to basic knowledge and clinical practice, as well as outlining the opportunities they offer for implementing the principles of the Three Rs (Replacement, Reduction and Refinement).

Intraepithelial dendritic cells and sensory nerves are structurally associated and functional interdependent in the cornea

The corneal epithelium consists of stratified epithelial cells, sparsely interspersed with dendritic cells (DCs) and a dense layer of sensory axons. We sought to assess the structural and functional correlation of DCs and sensory nerves. Two morphologically different DCs, dendriform and round-shaped, were detected in the corneal epithelium. The dendriform DCs were located at the sub-basal space where the nerve plexus resides, with DC dendrites crossing several nerve endings. The round-shaped DCs were closely associated with nerve fiber branching points, penetrating the basement membrane and reaching into the stroma. Phenotypically, the round-shaped DCs were CD86 positive. Trigeminal denervation resulted in epithelial defects with or without total tarsorrhaphy, decreased tear secretion, and the loss of dendriform DCs at the ocular surface. Local DC depletion resulted in a significant decrease in corneal sensitivity, an increase in epithelial defects, and a reduced density of nerve endings at the center of the cornea. Post-wound nerve regeneration was also delayed in the DC-depleted corneas. Taken together, our data show that DCs and sensory nerves are located in close proximity. DCs may play a role in epithelium innervation by accompanying the sensory nerve fibers in crossing the basement membrane and branching into nerve endings.

Effect of Hypoxia-regulated Polo-like Kinase 3 (Plk3) on Human Limbal Stem Cell Differentiation

Hypoxic conditions in the cornea affect epithelial function by activating Polo-like kinase 3 (Plk3) signaling and the c-Jun·AP-1 transcription complex, resulting in apoptosis of corneal epithelial cells. Hypoxic stress in the culture conditions also regulates limbal stem cell growth and fate. In this study, we demonstrate that there is a differential response of Plk3 in hypoxic stress-induced primary human limbal stem (HLS) and corneal epithelial (HCE) cells, resulting in different pathways of cell fate. We found that hypoxic stress induced HLS cell differentiation by down-regulating Plk3 activity at the transcription level, which was opposite to the effect of hypoxic stress on Plk3 activation to elicit HCE cell apoptosis, detected by DNA fragmentation and TUNEL assays. Hypoxic stress-induced increases in c-Jun phosphorylation/activation were not observed in HLS cells because Plk3 expression and activity were suppressed in hypoxia-induced HLS cells. Instead, hypoxic stress-induced HLS cell differentiation was monitored by cell cycle analysis and measured by the decrease and increase in p63 and keratin 12 expression, respectively. Hypoxic stress-induced Plk3 signaling to regulate c-Jun activity, resulting in limbal stem cell differentiation and center epithelial apoptosis, was also found in the corneas of wild-type and Plk3(-/-)-deficient mice. Our results, for the first time, reveal the differential effects of hypoxic stress on Plk3 activity in HLS and HCE cells. Instead of apoptosis, hypoxic stress suppresses Plk3 activity to protect limbal stem cells from death and to allow the process of HLS cell differentiation.

Putting on the brakes: Bacterial impediment of wound healing

The epithelium provides a crucial barrier to infection, and its integrity requires efficient wound healing. Bacterial cells and secretomes from a subset of tested species of bacteria inhibited human and porcine corneal epithelial cell migration in vitro and ex vivo. Secretomes from 95% of Serratia marcescens, 71% of Pseudomonas aeruginosa, 29% of Staphylococcus aureus strains, and other bacterial species inhibited epithelial cell migration. Migration of human foreskin fibroblasts was also inhibited by S. marcescens secretomes indicating that the effect is not cornea specific. Transposon mutagenesis implicated lipopolysaccharide (LPS) core biosynthetic genes as being required to inhibit corneal epithelial cell migration. LPS depletion of S. marcescens secretomes with polymyxin B agarose rendered secretomes unable to inhibit epithelial cell migration. Purified LPS from S. marcescens, but not from Escherichia coli or S. marcescens strains with mutations in the waaG and waaC genes, inhibited epithelial cell migration in vitro and wound healing ex vivo. Together these data suggest that S. marcescens LPS is sufficient for inhibition of epithelial wound healing. This study presents a novel host-pathogen interaction with implications for infections where bacteria impact wound healing and provides evidence that secreted LPS is a key factor in the inhibitory mechanism.

Alternatives to animal testing: A review

The number of animals used in research has increased with the advancement of research and development in medical technology. Every year, millions of experimental animals are used all over the world. The pain, distress and death experienced by the animals during scientific experiments have been a debating issue for a long time. Besides the major concern of ethics, there are few more disadvantages of animal experimentation like requirement of skilled manpower, time consuming protocols and high cost. Various alternatives to animal testing were proposed to overcome the drawbacks associated with animal experiments and avoid the unethical procedures. A strategy of 3 Rs (i.e. reduction, refinement and replacement) is being applied for laboratory use of animals. Different methods and alternative organisms are applied to implement this strategy. These methods provide an alternative means for the drug and chemical testing, up to some levels. A brief account of these alternatives and advantages associated is discussed in this review with examples. An integrated application of these approaches would give an insight into minimum use of animals in scientific experiments.

Ex vivo organotypic corneal model of acute epithelial herpes simplex virus type I infection

Herpes keratitis is one of the most severe pathologies associated with the herpes simplex virus-type 1 (HSV-1). Herpes keratitis is currently the leading cause of both cornea-derived and infection-associated blindness in the developed world. Typical presentation of herpes keratitis includes infection of the corneal epithelium and sometimes the deeper corneal stroma and endothelium, leading to such permanent corneal pathologies as scarring, thinning, and opacity. Corneal HSV-1 infection is traditionally studied in two types of experimental models. The in vitro model, in which cultured monolayers of corneal epithelial cells are infected in a Petri dish, offers simplicity, high level of replicability, fast experiments, and relatively low costs. On the other hand, the in vivo model, in which animals such as rabbits or mice are inoculated directly in the cornea, offers a highly sophisticated physiological system, but has higher costs, longer experiments, necessary animal care, and a greater degree of variability. In this video article, we provide a detailed demonstration of a new ex vivo model of corneal epithelial HSV-1 infection, which combines the strengths of both the in vitro and the in vivo models. The ex vivo model utilizes intact corneas organotypically maintained in culture and infected with HSV-1. The use of the ex vivo model allows for highly physiologically-based conclusions, yet it is rather inexpensive and requires time commitment comparable to that of the in vitro model.

Nuclear Factor-κB: central regulator in ocular surface inflammation and diseases

The nuclear factor-κB (NF-κB) is a key transcription factor pathway that is responsible for many key biological processes, such as inflammation, apoptosis, stress response, corneal wound healing, angiogenesis, and lymphangiogenesis. Numerous recent studies have investigated NF-κB in the context of ocular surface disorders, including chemical injury, ultraviolet radiation-induced injury, microbial infections, allergic eye diseases, dry eye, pterygium, and corneal graft rejection. The purpose this article is to summarize key findings with regard to the pathways regulating NF-κB and processes governed by the NF-κB pathway. In the innate defense system, NF-κB is involved in signaling from the toll-like receptors 2, 3, 4, 5 and 7, which are expressed in conjunctival, limbal, and corneal epithelial cells. These determine the ocular responses to infections, such as those caused by Pseudomonas aeruginosa, Staphylococcus aureus, adenovirus, and herpes simplex-1 virus. Natural angiogenic inhibitors enhance NF-κB, and this may occur through the mitogen-activated protein kinases and peroxisome proliferator-activated receptor γ. In alkali injury, inhibition of NF-κB can reduce corneal angiogenesis, suggesting a possible therapeutic strategy. The evaluation of NF-κB inhibitors in diseases is also discussed, including emodin, besifloxacin, BOL-303242-X (mapracorat), thymosin-β4, epigallocatechin gallate, Perilla frutescens leaf extract and IKKβ-targeting short interfering RNA.

Normal morphogenesis of epithelial tissues and progression of epithelial tumors

Epithelial cells organize into various tissue architectures that largely maintain their structure throughout the life of an organism. For decades, the morphogenesis of epithelial tissues has fascinated scientists at the interface of cell, developmental, and molecular biology. Systems biology offers ways to combine knowledge from these disciplines by building integrative models that are quantitative and predictive. Can such models be useful for gaining a deeper understanding of epithelial morphogenesis? Here, we take inventory of some recurring themes in epithelial morphogenesis that systems approaches could strive to capture. Predictive understanding of morphogenesis at the systems level would prove especially valuable for diseases such as cancer, where epithelial tissue architecture is profoundly disrupted.

Preservative use in topical glaucoma medications

Benzalkonium chloride (BAK) is the principal preservative employed in topical ocular hypotensive medications, although alternative compounds recently have begun to be employed or examined. Individual clinical trials have shown that exposure to BAK concentrations contained in ophthalmic solutions does not produce adverse sequelae in the majority of glaucoma patients, but concerns continue with regard to its long-term use. These concerns have resulted from an extensive research effort, including preclinical studies with in vitro and in vivo models, as well as recent clinical investigations dedicated specifically to this issue. The aim of this systematic literature review of both preclinical and clinical data was to determine the relevance of these findings to clinical practice. Most preclinical studies reported negative effects of BAK exposure, but with few exceptions, BAK concentrations and exposure times greatly exceeded those likely to be experienced by patients, given the normal physiological dilution by the tear film. In addition, consistent evidence of BAK-related toxicity did not emerge from our review of dedicated clinical investigations. Thus, taken together, current evidence supports the safety of BAK for most glaucoma patients, although subpopulations with abnormal tearing may benefit from alternative preservative compounds or preservative-free formulations. Further studies to identify these populations are needed.

Spontaneous bacterial keratitis in CD36 knockout mice

PURPOSE

CD36 is a Class B scavenger receptor that is constitutively expressed in the corneal epithelium and has been implicated in many homeostatic functions, including the homeostasis of the epidermal barrier. The aim of this study is to determine (1) whether CD36 is required for the maintenance of the corneal epithelial barrier to infection, and (2) whether CD36-deficient mice present with an increased susceptibility to bacterial keratitis.

METHODS

The corneas of CD36(-/-), TSP1(-/-), TLR2(-/-), and C57BL/6 WT mice were screened via slit lamp microscopy or ex vivo analysis. The epithelial tight junctions and mucin layer were assessed via LC-biotin and Rose Bengal staining, respectively. Bacterial quantification was performed on corneal buttons and GFP-expressing Staphylococcus aureus was used to study bacterial binding.

RESULTS

CD36(-/-) mice develop spontaneous corneal defects that increased in frequency and severity with age. The mild corneal defects were characterized by a disruption in epithelial tight junctions and the mucin layer, an infiltrate of macrophages, and increased bacterial binding. Bacterial quantification revealed high levels of Staphylococcus xylosus in the corneas of CD36(-/-) mice with severe defects, but not in wild-type controls.

CONCLUSIONS

CD36(-/-) mice develop spontaneous bacterial keratitis independent of TLR2 and TSP1. The authors conclude that CD36 is a critical component of the corneal epithelial barrier, and in the absence of CD36 the barrier breaks down, allowing bacteria to bind to the corneal epithelium and resulting in spontaneous keratitis. This is the first report of spontaneous bacterial keratitis in mice.

Plastic compressed collagen as a biomimetic substrate for human limbal epithelial cell culture

We describe, for the first time, the use of cellular plastic compressed collagen as a substrate for human limbal epithelial cell expansion and stratification. The characteristics of expanded limbal epithelial cells on either acellular collagen constructs or those containing human limbal fibroblasts were compared to a human central cornea control. After compression, human fibroblasts in collagen constructs remained viable and limbal epithelial cells were successfully expanded on the surface. After airlifting, a multilayered epithelium formed with epithelial cell morphology very similar to that of cells in the central cornea. Immunochemical staining revealed expression of basement membrane proteins and differentiated epithelial cell markers found in native central cornea. Ultrastructural analysis revealed cells on collagen constructs had many features similar to central cornea, including polygonal, tightly opposed surface epithelial cells with microvilli and numerous desmosomes at cell-cell junctions. Taken together, these data demonstrate that plastic compressed collagen constructs can form the basis of a biomimetic tissue model for in vitro testing and could potentially provide a suitable alternative to amniotic membrane as a substrate for limbal epithelial cell transplantation.

Corneal protection with high-molecular-weight hyaluronan against in vitro and in vivo sodium lauryl sulfate-induced toxic effects

PURPOSE

The aim of this study was to investigate high-molecular-weight hyaluronan (HA-HMW) corneal protection against sodium lauryl sulfate (SLS)-induced toxic effects with in vitro and in vivo experimental approaches.

METHODS

In vitro experiments consisted of a human corneal epithelial cell line incubated with HA-HMW, rinsed, and incubated with SLS. Cell viability, oxidative stress, chromatin condensation, caspase-3, -8, -9, and P2X7 cell death receptor activation, interleukin-6, and interleukin-8 production were investigated. In vivo experiments consisted of 36 New Zealand white rabbits treated for 3 days, 3 times per day, with HA-HMW or phosphate-buffered salt solution. At day 4, eyes were treated with SLS. Clinical observation and in vivo confocal microscopy using the Rostock Cornea Module of the Heidelberg Retina Tomograph-II were performed to evaluate and to compare SLS-induced toxicity between eyes treated with HA-HMW and eyes treated with phosphate-buffered salt solution.

RESULTS

In vitro data indicate that exposure of human corneal epithelial cells to HA-HMW significantly decreased SLS-induced oxidative stress, apoptosis, and inflammation cytokine production. In vivo data indicate that SLS cornea injuries, characterized by damaged corneal epithelium, damaged anterior stroma, and inflammatory infiltrations, were attenuated with HA-HMW treatment.

CONCLUSIONS

A good correlation was seen between in vitro and in vivo findings showing that HA-HMW decreases SLS-induced toxic effects and protects cornea.

Transepithelial corneal collagen cross-linking in keratoconus

PURPOSE

To evaluate the clinical effects of transepithelial corneal cross-linking (CXL) on keratoconic eyes pre-treated with substances enhancing epithelial permeability.

METHODS

Prospective, consecutive, single-masked, paired-eye study on 51 patients. The eye with more severe keratoconus was treated; the fellow eye served as the control. Gentamicin, benzalkonium chloride, and ethylenediaminetetraacetic acid were instilled for 3 hours, then oxybuprocaine for 30 minutes. Riboflavin 0.1% in 20% dextran T500 and oxybuprocaine were instilled for 30 minutes. Finally, ultraviolet A irradiation to the central 7.5 mm of the cornea was applied for 30 minutes, while riboflavin was instilled every 5 minutes.

RESULTS

Mean corrected distance visual acuity improved by 0.036 logMAR after CXL and worsened by 0.039 logMAR in the control eyes (P<.05). Safety index was 1.05 after CXL and 0.96 in the control group. Mean spherical equivalent refraction decreased by 0.35 D (less myopic) after CXL and increased by 0.83 diopters (D) in the control eyes (P<.05). Mean apex curvature on tangential videokeratography increased by 0.51 D after CXL and by 1.61 D in the control eyes (P=.16). Mean average simulated keratometry decreased by 0.10 D after CXL and increased by 0.88 D in the control eyes (P<.05). Mean index of surface variance increased (worsened) by 0.9 after CXL and 5.3 in the control eyes (P<.05). Mean endothelial cell density was unchanged.

CONCLUSIONS

A limited but favorable effect of transepithelial CXL was noted on keratoconic eyes, without complications. The effect appears to be less pronounced than described in the literature after CXL with de-epithelialization.

LL-37 via EGFR transactivation to promote high glucose-attenuated epithelial wound healing in organ-cultured corneas

Purpose. Patients with diabetes are at higher risk for delayed corneal reepithelialization and infection. Previous studies indicated that high glucose (HG) impairs epidermal growth factor receptor (EGFR) signaling and attenuates ex vivo corneal epithelial wound healing. The authors investigated the effects of antimicrobial peptide LL-37 on HG-attenuated corneal epithelial EGFR signaling and wound closure. Methods. Human corneal epithelial cells (HCECs) were stimulated with LL-37. Heparin-binding EGF-like growth factor (HB-EGF) shedding was assessed by measuring the release of alkaline phosphatase (AP) in a stable HCEC line expressing HB-EGF-AP. Activation of EGFR, phosphoinositide 3-kinase (PI3K), and extracellular signal-regulated kinases 1/2 (ERK1/2) was determined by Western blot analysis. Corneal epithelial wound closure was assessed in cultured HCECs and porcine corneas. LL-37 expression was determined by immune dot blot. Results. LL-37 induced HB-EGF-AP release and EGFR activation in a dose-dependent manner. LL-37 prolonged EGFR signaling in response to wounding. LL-37 enhanced the closure of a scratch wound in cultured HCECs and partially rescued HG-attenuated wound healing in an EGFR- and a PI3K-dependent manner and restored HG-impaired EGFR signaling in cultured porcine corneas. HG attenuated wounding-induced LL-37 expression in cultured HCECs. Conclusions. LL-37 is a tonic factor promoting EGFR signaling and enhancing epithelial wound healing in normal and high glucose conditions. With both antimicrobial and regenerative capabilities, LL-37 may be a potential therapeutic for diabetic keratopathy.

Novel cultured porcine corneal irritancy assay with reversibility endpoint

Several alternative assays exist to assess ocular irritancy without the use of live animals. However, these assays cannot address ocular injury reversibility. Reversibility is an issue critical to regulatory authorities and manufactures of commercial products, as ocular irritation caused by misuse or accidental exposure to a product may cause irreversible eye damage. Here we report the development and initial characterization of a novel ocular irritation assay that addresses ocular injury reversibility. This assay, the Porcine Corneal Ocular Reversibility Assay (PorCORA), uses an air-interface porcine corneal culture system to sustain ex vivo porcine corneas as a model system. These corneas are maintained in culture for 21 days to determine if cornea injury, once inflicted, will reverse. Corneal injury reversibility is measured using Sodium Fluorescein (NaFl) stain to detect compromised epithelial barrier function. In this study, we examined the effects of five compounds on the cultured corneas: phosphate-buffered saline (PBS), 100% Ethanol (EtOH), 3% Sodium Dodecyl Sulfate (SDS), 1% Benzalkonium Chloride (BAK), and 10% Sodium Hydroxide (NaOH). Overall, the persistence of corneal effects between historical Draize rabbit eye data and PorCORA indicates a correlation coefficient of 0.98 (for the five compounds tested) and a correlation coefficient of 0.97 with the Draize modified maximal average score (MMAS). Finally, both fluorescence confocal microscopy and histopathology evidence demonstrates that the PorCORA and NaFl measurements are indicative of actual cellular and tissue damage. PorCORA shows promise as a potential non-animal replacement assay capable of predicting ocular damage reversibility.

Extent of Corneal Injury as a Biomarker for Hazard Assessment and the Development of Alternative Models to the Draize Rabbit Eye Test

We have characterized 22 ocular irritants differing in type (surfactants, acid, alkali, bleaches, alcohol, aldehyde, acetone) and severity (slight to severe) by using the low-volume rabbit eye test. Ocular irritation was evaluated by 1) light microscopy to assess pathological changes, 2) in vivo confocal microscopy (CM) to quantify 4-dimensionally (x, y, z, and t) initial corneal injury and later responses in the same eye, and 3) laser scanning CM to quantify initial cell death. These studies revealed that regardless of the processes leading to injury, slight irritants injure the corneal epithelium, mild irritants injure the corneal epithelium and the superficial stroma, and moderate/severe irritants injure the epithelium, deep stroma, and at times the corneal endothelium. Furthermore, extent of initial corneal injury was shown to predict subsequent responses and final outcomes. These findings suggest that extent of corneal injury may be used as a basis for the development of alternative ocular irritation tests. To test the validity of this approach, we have used an ex vivo, rabbit cornea culture model to measure extent of corneal injury following exposure to ocular irritants. Data indicate that the extent of ex vivo corneal injury significantly correlate with the extent of initial injury measured previously in live animals. Overall, these findings indicate that extent of initial corneal injury can be used as a new "gold standard" for the continued refinement and ultimate replacement of the Draize rabbit eye Ocular Irritation Test.

Role of small GTPase Rho in regulating corneal epithelial wound healing

PURPOSE

To determine the role of small GTPase Rho and its relation with epidermal growth factor receptor (EGFR) in mediating corneal epithelial wound healing.

METHODS

Rho activity in THCE cells, an SV40-immortalized human corneal epithelial cell (HCEC) line, and primary HCECs was assessed by pull-down assay followed by Western blotting. Rho functions were inhibited with specific inhibitor exoenzyme C3 (C3) and confirmed by knockdown with small interference RNA (siRNA) transfection. Effects of Rho inhibition on wound healing were determined in porcine corneal organ culture and HCEC scratch wound models. Effects of C3 on cell proliferation and focal adhesion formation were determined by BrdU incorporation assay and immunocytochemistry, respectively.

RESULTS

Wounding, lysophosphatidic acid, and heparin-binding EGF-like growth factor (HB-EGF) induced rapid and strong RhoA activation. HB-EGF-, but not wounding-, enhanced RhoA activity was sensitive to EGFR inhibition. In corneal organ and cell culture models, C3 attenuated spontaneous and HB-EGF-induced wound closures, confirmed by delayed wound healing in cells transfected with RhoA siRNA. C3 also retarded spontaneous wound healing in the presence of hydroxyurea, a cell cycle blocker. C3 significantly reduced the number of BrdU-positive cells near the leading edge. Treatment with C3 resulted in the disruption of the cortical actin cytoskeleton and in the disappearance of paxillin-containing focal adhesion and lamellipodia.

CONCLUSIONS

Wounding induces RhoA activation through an EGFR-independent pathway. Rho activity is required for modulating cell migration and proliferation through cytoskeleton reorganization and focal adhesion formation in response to wounding.

Effects of Topical Antiglaucoma Medications on Corneal Epithelium as Evaluated by Gene Expression Patterns

PURPOSE

To examine the expression pattern of the stress-related genes c-fos and c-jun, which encode the 2 major components of activator protein (AP)-1, and cyclooxygenase (COX)-2 in rat corneal epithelium treated with topical antiglaucoma medications and benzalkonium chloride (BAK) preservative.

METHODS

Eighty-eight male Wistar rats were used. We instilled antiglaucoma eye drops (0.5% Timoptol, 0.005% Xalatan, or 0.12% Rescula), their chemical constituents (active ingredients), or BAK preservative (0.005%, 0.01%, or 0.02%) in 1 eye of each rat. Fellow eyes served as controls. The eyes were enucleated after various intervals. In situ hybridization and immunohistochemistry were used to detect expression of c-fos, c-jun, and COX-2.

RESULTS

Expression of c-fos, c-jun, and COX-2 was minimally observed in uninjured rat corneal epithelium. Thirty minutes to 1 hour after applying the antiglaucoma eye drops, signals for c-fos and c-jun mRNA were detected in the corneal epithelium. Ninety minutes after applying 0.005% Xalatan, 0.12% Rescula, or their chemical constituents, but not 0.5% Timoptol, COX-2 was detected in corneal epithelium. Expression of c-fos and c-jun seemed more marked with prostaglandins than with timolol. Thirty minutes to 1 hour after instillation of 0.02% BAK preservative, signals for c-fos and c-jun mRNA were detected in the corneal and conjunctival epithelium. COX-2 was not induced by 0.5% Timoptol or BAK preservative. COX-2 mRNA was not affected by applying 0.005% or 0.01% BAK preservative. Proteins of these components were also detected, indicating that each mRNA expression was followed by protein synthesis.

CONCLUSIONS

Corneal and conjunctival epithelial cells are transcriptionally activated transiently at an early phase after topical administration of antiglaucoma medications and BAK preservative. Stimulatory effects of prostaglandin drugs on corneal epithelial cells were more marked than those with timolol. Expression of COX-2 may potentially be involved in inflammatory response in the corneal epithelium.

Inflammation in dry eye

Dry eye is a condition of altered tear composition that results from a diseased or dysfunctional lacrimal functional unit. Evidence suggests that inflammation causes structural alterations and/or functional paralysis of the tear-secreting glands. Changes in tear composition resulting from lacrimal dysfunction, increased evaporation and/or poor clearance have pro-inflammatory effects on the ocular surface. This inflammation is responsible in part for the irritation symptoms, ocular surface epithelial disease, and altered corneal epithelial barrier function in dry eye. Anti-inflammatory therapies for dry eye target one or more of the inflammatory mediators/pathways that have been identified in dry eye.

In vitro alternatives to the use of animals in ocular toxicology testing

Chemical substances, including household products, industrial chemicals, and cosmetics, must be tested for ocular toxicity or irritancy so that the public can be assured of their safety or warned of dangers associated with their use. The in vivo Draize test is the standard method used to meet this requirement; however, this test is coming under increasing criticism on scientific and ethical grounds. This has led to the development of a large number of proposed in vitro tests, some of which are routinely used to screen chemicals in toxicology laboratories. This review addresses regulations governing ocular irritancy testing and the current status of the movement toward use of alternative methods. Such methods include the use of cultured cells, hen's eggs, isolated animal eyes and corneas, human corneal epithelial cell lines, and the recently developed in vitro corneal equivalent models. The protocols for these methods are outlined, and their endpoints are described with respect to prediction of in vivo responses. The tests are evaluated in the context of the outcomes of validation studies and acceptance by regulatory agencies. While several of these tests yield useful information concerning ocular irritancy, to date, no in vitro alternative test has been validated as a replacement for the Draize test. If the goal of replacing the in vivo test while protecting the public from chemical eye injury is to be achieved, further development and improvement of alternative tests, as well as establishment of a human ocular toxicity data base, are required.

Lysophosphatidic acid promoting corneal epithelial wound healing by transactivation of epidermal growth factor receptor

PURPOSE

To identify the underlying mechanisms by which lipid mediator lysophosphatidic acid (LPA) acts as a growth factor in stimulating extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3'-kinase (PI3K) during corneal epithelial wound healing.

METHODS

Epithelial debridement wounds in cultured porcine corneas and scratch wounds in an epithelial monolayer of SV40-immortalized human corneal epithelial (THCE) cells were allowed to heal in the presence or absence of an epidermal growth factor receptor (EGFR) inhibitor (tyrphostin AG1478), a matrix metalloproteinase inhibitor (GM6001), or a heparin-binding EGF-like growth factor (HB-EGF) antagonist (CRM197) with or without LPA. EGFR activation was analyzed by immunoprecipitation using EGFR antibodies and Western blotting with phosphotyrosine antibodies. Phosphorylation of ERK and AKT (a major substrate of PI3K) was analyzed by Western blotting with antibodies specific to the phosphorylated proteins. Wound- and LPA-induced shedding of HB-EGF was assessed by measuring the release of alkaline phosphatase (AP) in a stable THCE cell line that expressed HB-EGF with AP inserted in the heparin-binding site.

RESULTS

In organ and cell culture models, LPA enhanced corneal epithelial wound healing. LPA-stimulated and spontaneous wound closure was attenuated by AG1478, GM6001, or CRM197. Consistent with the effects on epithelial migration, these inhibitors, as well as the Src kinase inhibitor (PP2), retarded LPA-induced activation of EGFR and its downstream effectors ERK and AKT in THCE cells. Unlike exogenously added HB-EGF, LPA stimulated moderate EGFR phosphorylation; the level of phosphorylated EGFR was similar to that induced by wounding. However, LPA appeared to prolong wound-induced EGFR signaling. The release of HB-EGF assessed by AP activity increased significantly in response to wounding, LPA, or both, and the release of HB-EGF-AP induced by LPA was inhibited by PP2 and GM6001.

CONCLUSIONS

LPA accelerates corneal epithelial wound healing through its ability to induce autocrine HB-EGF signaling. Transactivation of EGFR by LPA represents a convergent signaling pathway accessible to stimuli such as growth factors and ligands of G-protein-coupled receptors in response to pathophysiological challenge in human corneal epithelial cells.

Examination of the restoration of epithelial barrier function following superficial keratectomy

The goal of the present study was to determine the rate of restoration of the corneal epithelial barrier following a superficial keratectomy using a functional assay of tight junction integrity. Adult Sprague-Dawley rats were anesthetized and a 3-mm superficial keratectomy was performed. The eyes were allowed to heal from 4 h to 8 weeks and the rate of epithelial wound closure was determined. To examine the restoration of the barrier function, EZ-Link Sulfo-NHS-LC-Biotin (LC-Biotin) was applied to all eyes, experimental and control, for 15 min at the time of sacrifice. This compound does not penetrate through intact tight junctions. Indirect immunofluorescence was performed with anti-laminin, a marker of basement membrane; fluorescein-conjugated streptavidin to detect the biotinylated marker; and anti-occludin and anti-ZO-1, markers of tight junctions. Epithelial wound closure was observed at 36-42 h after wounding. LC-Biotin did not penetrate the intact epithelium. Upon wounding, LC-Biotin penetrated into the stroma subjacent and slightly peripheral to the wound area. This pattern was present from 4-48 h post-wounding. The area of LC-Biotin localization decreased with time and the functional barrier was restored by 72 h. Occludin and ZO-1 were present at all time points. The number of cell layers expressing these proteins appeared to increase at 48 and 72 h. Continuous laminin localization was not observed until at least 7 days after wounding. Barrier function is restored within 1-1.5 days after epithelial wound closure. The loss of barrier function does not extend beyond the edge of the original wound. The restoration of barrier function does not appear to correlate with reassembly of the basement membrane in this model.

Corneal NF-kappaB activity is necessary for the retention of transparency in the cornea of UV-B-exposed transgenic reporter mice

To determine the dynamics of Nuclear Factor-kappaB (NF-kappaB) in murine corneal pathology and the role of NF-kappaB in maintaining corneal clarity after ultraviolet B radiation insult, transgenic mice containing NF-kappaB-luciferase reporter were exposed to LPS (bacterial lipopolysaccharide), TNF-alpha (Tumor Necrosis Factor-alpha) or 4 kJ m(-2) UV-B radiation. NF-kappaB decoy oligonucleotides were also administered in some of the UV-B experiments. Following various exposure times, the mice were sacrificed and whole eyes or corneal tissues were obtained. Whole eyes were examined for scattering using a point-source optical imaging technique. Tissue homogenates were examined for luciferase activity using a luminometer. TNF-alpha and LPS-injected NF-kappaB-luciferase transgenic mice demonstrated 3-10-fold increases in cornea NF-kappaB with peak activities at 4 and 6 hr post-injection, respectively. Mice exposed to 4 kJ m(-2) UV-B exhibited a 3-fold increase in NF-kappaB activity 4 hr post-exposure. The administration of NF-kappaB-decoy oligonucleotides to mice had the effect of reducing UV-B-induced NF-kappaB activity in the cornea and significantly increasing the amount of light scattering in UV-B exposed corneas 7 days post-UV-B exposure when compared to sham injected mice. These results indicate that NF-kappaB is activated in cornea in pathologies that involves increased plasma levels of LPS and TNF-alpha, as well as direct UV-B exposure, and suggest that NF-kappaB activation play an essential part in the corneal healing process.

Altered expression of aquaporins in bullous keratopathy and Fuchs' dystrophy corneas

Corneas with edema-related diseases lose transparency, which causes significant vision loss. This study analyzed seven aquaporins (AQPs) in normal corneas, pseudophakic/aphakic bullous keratopathy (PBK/ABK) corneas, Fuchs' dystrophy corneas, keratoconus corneas, post-cataract surgery (PCS) corneas, and normal organ-cultured corneas. RNA levels for AQP1, AQP4, and beta2-microglobulin were measured by RT-PCR. AQP1 antibody localized to stromal cells of all corneas. PBK/ABK and Fuchs' dystrophy corneas had decreased endothelial cell staining compared with normal. AQP1 mRNA was found in whole corneas and cultured stromal fibroblasts but not in isolated epithelial cells. AQP3 staining was found in basal epithelial cells of the normal, Fuchs' dystrophy, and keratoconus corneas but throughout the entire epithelium of PBK/ABK corneas. AQP4 antibody localized to endothelial cells of all corneas and in stromal cells of PBK/ABK corneas. AQP4 mRNA was identified in whole human corneas. AQP5 was found in epithelial cells of all corneas. AQP0, AQP2, and AQP9 were not found in any corneas. Normal AQP distributions were found in PCS and organ-cultured corneas, although they showed signs of swelling. Our study demonstrates that AQP abnormalities are found in PBK/ABK corneas (decreased AQP1, increased AQP3 and AQP4) and Fuchs' dystrophy corneas (decreased AQP1). Although both have vision-disrupting corneal edema, the mechanisms of fluid accumulation may be different in each disease.

Wound-induced HB-EGF ectodomain shedding and EGFR activation in corneal epithelial cells

PURPOSE

Epithelial wound healing is, at least in part, mediated in an autocrine fashion by epidermal growth factor (EGF) receptor (EGFR)-ligand interactions. This study sought to identify the endogenous EGFR ligand and the mechanism by which it is generated in response to wounding in cultured porcine corneas and human corneal epithelial cells.

METHODS

Epithelial debridement wounds in cultured porcine corneas and scratch wounds in an epithelial monolayer of SV40-immortalized human corneal epithelial (THCE) cells were allowed to heal in the presence of tyrphostin AG1478 (an EGFR inhibitor), GM6001 (a matrix metalloproteinase [MMP] inhibitor), or CRM197 (a diphtheria toxin mutant), with or without HB-EGF. The activation of EGFR and extracellular signal-regulated kinase (ERK) was analyzed by immunoprecipitation using EGFR antibodies and Western blot analysis with phosphotyrosine antibody. Wound induced HB-EGF shedding was assessed by isolation of secreted HB-EGF from wounded THCE cells and by measuring the release of alkaline phosphatase (AP) in THCE stable cell lines expressing HB-EGF-AP.

RESULTS

In THCE cells, wound-induced EGFR phosphorylation and ERK activation. In both organ and cell culture models, epithelial wounds were healed in basal media and inhibition of EGFR activation by AG1478 blocked wound closure with or without exogenously added HB-EGF. GM6001 delayed wound closure. Its effects diminished in the presence of exogenous EGF or HB-EGF, suggesting that the MMP inhibitor primarily blocks the release of EGFR ligands. CRM197, a highly specific antagonist of HB-EGF, impaired epithelial wound closure, suggesting that HB-EGF is an endogenous ligand released on epithelial wounding. Consistent with the effects on epithelial migration, all inhibitors as well as HB-EGF function-blocking antibodies retarded wound-induced EGFR phosphorylation in cultured THCE cells. The release of HB-EGF in response to wounding was demonstrated by the fact that heparin-binding proteins isolated from wounded, but not control, THCE-conditioned medium stimulated EGFR and ERK phosphorylation and by the expression of HB-EGF-AP in THCE cells, in which wounding induced the release of AP activity in an MMP-inhibitor-sensitive manner.

CONCLUSIONS

HB-EGF released on wounding acts as an autocrine-paracrine EGFR ligand. HB-EGF shedding and EGFR activation represent a critical event during corneal epithelial wound healing, suggesting a possible manipulation of wound healing during the early phases.