Effects of growth factors on corneal wound healing

Adverse effects of anti-cancer biologics on the ocular surface

PURPOSE OF REVIEW

Cancer immunotherapy is one of the most emerging and rapidly growing fields.Ocular side effects associated with these therapies are common and can be present in up to 70% of patients.The cornea may be involved in different pathogenic mechanisms triggered by different immunotherapeutic agents, and corneal disease varies from mild symptoms to severe corneal ulceration and melting with visual loss.We aimed to review the incidence, mechanism, and management of ocular surface side effects in cancer patients receiving immunotherapy.

RECENT FINDINGS

With the recent use of immunotherapeutic agents in cancer patients, in particular immune checkpoint inhibitors (ICIs) and epidermal growth factor receptor (EGFR) inhibitors, ocular surface and corneal involvement are common side effects.These patients can be at risk of sight threatening complications that warrant prompt diagnosis and careful monitoring and management.

SUMMARY

Immunotherapy- related corneal complications in cancer patients are associated with a decreased quality of life. Prompt recognition and an interdisciplinary approach between ophthalmologists and oncologists are crucial to handle immune related ocular adverse events in these patients, in order to maintain ocular surface integrity and avoid a vision threatening complication.

Medrysone promotes corneal injury repair by promoting M2-like polarization of macrophages

BACKGROUND

Accumulated evidence suggests that M2-like polarized macrophages plays an important role in reducing inflammation, promoting and accelerating wound healing process and tissue repair. Thus, M2-like TAMs (Tumour-associated macrophages) was an appealing target for therapy intervention.

METHOD

Flow cytometry and RT-PCR assay were used to detect the polarization of macrophages induced by Medrysone, and the rat corneal mechanical injury model was established to evaluate the efficacy of Medrysone in cornel repair.

RESULTS

Here we found that Medrysone enhanced IL-4 induced M2 polarization of macrophages, as illustrated by increased expression of CD206, up-regulation of M2 marker mRNAs. Medrysone promoted VEGF and CCL2 secretion in IL-4 induced M2-like polarization. IL-4 triggered STAT6 activation was further enhanced by Medrysone and silencing of STAT6 partially abrogated the stimulatory effect of Medrysone. Medrysone improved migration-promoting feature of M2-like macrophages, as indicated by increased migration of endothelial cells. Further, Medrysone promoted corneal injury repair by inducing M2 polarization of macrophages in vivo.

CONCLUSION

Our study suggest that Medrysone promotes corneal injury repair by inducing the M2 polarization of macrophages, providing a theoretical basis for the application of Medrysone in the treatment of corneal injury.

Nano Self-Assemblies of Caffeic Acid-Fibronectin Mimic a Peptide Conjugate for the Treatment of Corneal Epithelial Injury

Rapid corneal re-epithelialization is important for corneal wound healing. Corneal epithelial cell motility and oxidative stress are important targets for therapeutic intervention. In this study, we covalently conjugated the antioxidant caffeic acid (CA) with a bioactive peptide sequence (PHSRN) to generate a CA-PHSRN amphiphile, which was formulated into nanoparticular eye drops with an average size of 43.21 ± 16 nm. CA-PHSRN caused minimal cytotoxicity against human corneal epithelial cells (HCECs) and RAW264.7 cells, exhibited an excellent free radical scavenging ability, and remarkably attenuated reactive oxygen species (ROS) levels in H2O2-stimulated HCECs. The antioxidant and anti-inflammatory activities of CA-PHSRN were assessed in lipopolysaccharide (LPS)-stimulated RAW264.7 cells. The results show that CA-PHSRN treatment effectively prevented LPS-induced DNA damage and significantly reduced the levels of LPS-induced pro-inflammatory cytochemokines (i.e., iNOS, NO, TNF-α, IL-6, and COX-2) in a dose-dependent manner. Moreover, using a rabbit corneal epithelial ex vivo migration assay, we demonstrated that the proposed CA-PHSRN accelerated corneal epithelial cell migration and exhibited high ocular tolerance and ocular bioavailability after topical instillation. Taken together, the proposed CA-PHSRN nanoparticular eye drops are a promising therapeutic formulation for the treatment of corneal epithelial injury.

Comparison of epitheliotrophic factors in platelet-rich plasma versus autologous serum and their treatment efficacy in dry eye disease

Current treatment of severe dry eye disease (DED) includes blood-derived eye drops, such as autologous serum (AS), which lubricate the eyes and provide factors that improve ocular surface and aid in wound healing. Recent studies indicated that platelet-rich plasma (PRP) was also effective. This study aims to compare the concentration and stability of epitheliotrophic factors in AS and PRP and their efficacy in DED patients. Epitheliotrophic factors of interest are epidermal growth factor (EGF), fibronectin, platelet-derived growth factor-AB (PDGF-AB), and transforming growth factor-beta1 (TGF-β1). We determined that all epitheliotrophic factors were present in AS and PRP at baseline and did not decrease in concentrations in all storage conditions (4 °C for 1 week and at − 20 °C for 1 and 3 months). However, differences in concentrations in AS and PRP were observed. PRP was also shown not to be inferior to AS in terms of efficacy in DED treatment in a prospective randomized control trial which evaluated ocular surface disease index, dry eye questionnaire, ocular surface staining, tear breakup time, and Schirmer test at baseline and at 1-month follow-up. Therefore, with its shorter preparation time, PRP could be considered as an alternative to AS for the treatment of DED.

Intravitreal application of epidermal growth factor in non-exudative age-related macular degeneration

PURPOSE

To assess the safety of intravitreally applied epidermal growth factor (EGF).

METHODS

The clinical interventional, prospective, single-centre, case series study included patients with age-related macular degeneration-related geographic atrophy (GA), in whom the eye with the worse best-corrected visual acuity (BCVA) underwent a single, or repeated, intravitreal injection of EGF (0.75 µg in 50 µL). At baseline and afterwards, the eyes underwent ophthalmological examinations.

RESULTS

The study included seven patients (mean age:70.0±12.2 years (range: 54-86 years), with five patients receiving a single injection and two patients receiving two intravitreal injections in an interval of 4 weeks. Mean duration of follow-up was 97±97 days (median:35 days; range: 7-240 days). Mean BCVA was lower at baseline than at study end (1.41±0.44 logMAR vs 0.97±0.12 logMAR; p=0.03). Mean size of the GA lesions did not differ significantly between baseline and study end (29 212±22 887 pixels vs 29 300±22 905 pixels; p=0.59) nor did the mean perimetric mean defect (-10.3±5.9 dB vs 12.0±8.8 dB; p=0.35) or the electroretinographical b-wave amplitude (44.53±31.7 µV vs 64.5±25.5 µV; p=0.12). After a second injection 4 weeks after the first injection, one of two patients developed a cystoid macular oedema in association with an induced incomplete posterior vitreous detachment. It persisted for 3 weeks. Visual acuity in this eye improved from 1.0 logMAR at baseline to 0.80 logMAR at study end.

CONCLUSIONS

Except for one eye with temporary, self-resolving cystoid macular oedema, single and repeated intravitreal applications of EGF (0.75 µg) in patients with GA did not lead to intraocular inflammations or any observed intraocular side effect.

TRIAL REGISTRATION NUMBER

ISRCTN12733334.

Topical Umbilical Cord Serum for Corneal Epithelial Defects after Diabetic Vitrectomy

Purpose

To evaluate the role of topical umbilical cord serum (TUCS) therapy in treating corneal epithelial defects (CEDs) after diabetic vitrectomy.

Methods

In this double-masked, randomized clinical trial, we included 80 eyes of 80 patients who were candidates for vitrectomy due to proliferative diabetic retinopathy complications. In cases of corneal edema obscuring the fundus view during surgery, the corneal epithelium was removed using a 6-mm trephine and a blade no.15. The day after the surgery, patients were randomly divided into two groups: (1) the TUCS group that received 20% TUCS six times/day in addition to the conventional treatment of CED and (2) the control group, which was prescribed artificial tears as placebo in addition to the conventional treatment of CED. The rate of healing of CEDs was measured via two maximum linear dimensions perpendicular to each other at the start of therapy and on postoperative days 1-5, 7, and 12.

Results

Of 80 eyes, 40 were assigned to each treatment group. The mean times to complete CED healing were 2.4 ± 0.7 and 3.8 ± 2.1 days in the TUCS and control groups, respectively (P < 0.001). Persistent CED occurred in two eyes in the control group but in no eyes in the TUCS group.

Conclusion

TUCS therapy may be safe and effective in healing CEDs after vitrectomy in patients with diabetes.

Role of Bone Morphogenetic Protein 7 (BMP7) in the Modulation of Corneal Stromal and Epithelial Cell Functions

In the cornea, healing of the wounded avascular surface is an intricate process comprising the involvement of epithelial, stromal and neuronal cell interactions. These interactions result to the release of various growth factors that play prominent roles during corneal wound healing response. Bone morphogenetic proteins (BMPs) are unique multi-functional potent growth factors of the transforming growth factor-beta (TGF-β) superfamily. Treatment of corneal epithelial cells with substance P and nerve growth factor resulted to an increase in the expression of BMP7 mRNA. Since BMP7 is known to modulate the process of corneal wound healing, in this present study, we investigated the influence of exogenous rhBMP7 on human corneal epithelial cell and stromal cell (SFs) function. To obtain a high-fidelity expression profiling of activated biomarkers and pathways, transcriptome-wide gene-level expression profiling of epithelial cells in the presence of BMP7 was performed. Gene ontology analysis shows BMP7 stimulation activated TGF-β signaling and cell cycle pathways, whereas biological processes related to cell cycle, microtubule and intermediate filament cytoskeleton organization were significantly impacted in corneal epithelial cells. Scratch wound healing assay showed increased motility and migration of BMP7 treated epithelial cells. BMP7 stimulation studies show activation of MAPK cascade proteins in epithelial cells and SFs. Similarly, a difference in the expression of claudin, Zink finger E-box-binding homeobox 1 was observed along with phosphorylation levels of cofilin in epithelial cells. Stimulation of SFs with BMP7 activated them with increased expression of α-smooth muscle actin. In addition, an elevated phosphorylation of epidermal growth factor receptor following BMP7 stimulation was also observed both in corneal epithelial cells and SFs. Based on our transcriptome analysis data on epithelial cells and the results obtained in SFs, we conclude that BMP7 contributes to epithelial-to-mesenchymal transition-like responses and plays a role equivalent to TGF-β in the course of corneal wound healing.

The Role of the Lysyl Oxidases in Tissue Repair and Remodeling: A Concise Review

Tissue injury provokes a series of events containing inflammation, new tissue formation and tissue remodeling which are regulated by the spatially and temporally coordinated organization. It is an evolutionarily conserved, multi-cellular, multi-molecular process via complex signalling network. Tissue injury disorders present grievous clinical problems and are likely to increase since they are generally associated with the prevailing diseases such as diabetes, hypertension and obesity. Although these dynamic responses vary not only for the different types of trauma but also for the different organs, a balancing act between the tissue degradation and tissue synthesis is the same. In this process, the degradation of old extracellular matrix (ECM) elements and new ones' synthesis and deposition play an essential role, especially collagens. Lysyl oxidase (LOX) and four lysyl oxidase-like proteins are a group of enzymes capable of catalyzing cross-linking reaction of collagen and elastin, thus initiating the formation of covalent cross-links that insolubilize ECM proteins. In this way, LOX facilitates ECM stabilization through ECM formation, development, maturation and remodeling. This ability determines its potential role in tissue repair and regeneration. In this review, based on the current in vitro, animal and human in vivo studies which have shown the significant role of the LOXs in tissue repair, e.g., tendon regeneration, ligament healing, cutaneous wound healing, and cartilage remodeling, we focused on the role of the LOXs in inflammation phase, proliferation phase, and tissue remodeling phase of the repair process. By summarizing its healing role, we hope to shed light on the understanding of its potential in tissue repair and provide up to date therapeutic strategies towards related injuries.

Molecular insights on the effect of TGF-β1/-β3 in human corneal fibroblasts

Transforming growth factor β (TGF-β) plays a critical role in wound healing and the pathogenesis of fibrosis (scarring). Three isoforms of TGF-β have been identified in mammals. Previous studies have shown that the addition of TGF-β1 (T1) or -β2 (T2) to human corneal fibroblasts (HCF) cultured in a 3-dimensional construct resulted in a fibrotic matrix, while the addition of TGF-β3 (T3) resulted in the production of enhanced non-fibrotic matrix as compared to control (Vitamin C [VitC] only). In the current investigation, we undertook the molecular comparison of fibrosis-related gene expression in T1 or T3-treated HCF to gain further insights into the regulation and roles of these two isoforms on the fibrotic response. HCF were cultured in 100 mm dishes in basic medium (Eagles minimum essential medium [EMEM] with 10% fetal bovine serum [FBS]). At 70-80% confluency, cells were exposed to basic medium with 0.5 mM 2-O-α-d-glucopyranosyl-l-ascorbic acid (VitC) ± 2 ng/ml of T1 or T3. After 4 h or 3 days, cells were harvested, and mRNA or protein was isolated. Fibrosis related mRNA levels were assayed using a commercial qRT-PCR Array. Selected proteins were examined using Western blotting (WB). Experiments were performed 6 times for the qRT-PCR and 4 times for WB for each condition. qRT-PCR results showed that most of the fibrosis-related genes were up or downregulated in HCF exposed to T1 or T3 as compared with VitC control. At 4 h, only Smad7 expression was significantly altered in T3-treated HCF, compared to T1, and at 3 days, five genes were altered. WB confirmed that T1 significantly decreased Smad7 expression compared to T3 and control, and that the expression of thrombospondin-1 in T3-stimulated HCF was enhanced compared to T1-treated cells. Finally, both T1 and T3 decreased Smad3 expression dramatically at both time points. At early time points, T1 and T3 have similar effects on expression of fibrosis related genes; however, with a longer exposure, an increasing number of genes were differentially expressed. Interestingly, most of the differentially expressed gene products are secreted by the cells and may be related to the modulation of extracellular matrix.

Estimating cell diffusivity and cell proliferation rate by interpreting IncuCyte ZOOM™ assay data using the Fisher-Kolmogorov model

Background

Standard methods for quantifying IncuCyte ZOOM™ assays involve measurements that quantify how rapidly the initially-vacant area becomes re-colonised with cells as a function of time. Unfortunately, these measurements give no insight into the details of the cellular-level mechanisms acting to close the initially-vacant area. We provide an alternative method enabling us to quantify the role of cell motility and cell proliferation separately. To achieve this we calibrate standard data available from IncuCyte ZOOM™ images to the solution of the Fisher-Kolmogorov model.

Results

The Fisher-Kolmogorov model is a reaction-diffusion equation that has been used to describe collective cell spreading driven by cell migration, characterised by a cell diffusivity, D, and carrying capacity limited proliferation with proliferation rate, λ, and carrying capacity density, K. By analysing temporal changes in cell density in several subregions located well-behind the initial position of the leading edge we estimate λ and K. Given these estimates, we then apply automatic leading edge detection algorithms to the images produced by the IncuCyte ZOOM™ assay and match this data with a numerical solution of the Fisher-Kolmogorov equation to provide an estimate of D. We demonstrate this method by applying it to interpret a suite of IncuCyte ZOOM™ assays using PC-3 prostate cancer cells and obtain estimates of D, λ and K. Comparing estimates of D, λ and K for a control assay with estimates of D, λ and K for assays where epidermal growth factor (EGF) is applied in varying concentrations confirms that EGF enhances the rate of scratch closure and that this stimulation is driven by an increase in D and λ, whereas K is relatively unaffected by EGF.

Conclusions

Our approach for estimating D, λ and K from an IncuCyte ZOOM™ assay provides more detail about cellular-level behaviour than standard methods for analysing these assays. In particular, our approach can be used to quantify the balance of cell migration and cell proliferation and, as we demonstrate, allow us to quantify how the addition of growth factors affects these processes individually.

Novel Therapy to Treat Corneal Epithelial Defects: A Hypothesis with Growth Hormone

Impaired corneal wound healing that occurs with ocular surface disease, trauma, systemic disease, or surgical intervention can lead to persistent corneal epithelial defects (PCED), which result in corneal scarring, ulceration, opacification, corneal neovascularization, and, ultimately, visual compromise and vision loss. The current standard of care can include lubricants, ointments, bandage lenses, amniotic membranes, autologous serum eye drops, and corneal transplants. Various inherent problems exist with application and administration of these treatments, which often may not result in a completely healed surface. A topically applicable compound capable of promoting corneal epithelial cell proliferation and/or migration would be ideal to accelerate healing. We hypothesize that human growth hormone (HGH) is such a compound. In a recent study, HGH was shown to activate signal transducer and activators of transcription-5 (STAT5) signaling and promote corneal wound healing by enhancing corneal epithelial migration in a co-culture system of corneal epithelial cells and fibroblasts. These effects require an intact communication between corneal epithelia and fibroblasts. Further, HGH promotes corneal wound healing in a rabbit debridement model, thus demonstrating the effectiveness of HGH in vivo as well. In conclusion, HGH may represent an exciting and effective topical therapeutic to promote corneal wound healing.

Peptide therapies for ocular surface disturbances based on fibronectin-integrin interactions

The condition of the corneal epithelium is a critical determinant of corneal transparency and clear vision. The corneal epithelium serves as a barrier to protect the eye from external insults, with its smooth surface being essential for its optical properties. Disorders of the corneal epithelium include superficial punctate keratopathy, corneal erosion, and persistent epithelial defects (PEDs). The prompt resolution of these disorders is important for minimization of further damage to the cornea. Currently available treatment modalities for corneal epithelial disorders are based on protection of the ocular surface in order to allow natural healing to proceed. PEDs remain among the most difficult corneal conditions to treat, however. On the basis of characterization of the pathobiology of PEDs at the cell and molecular biological levels, we have strived to develop new modes of treatment for these defects. These treatments rely on two key concepts: provision of a substrate, such as the adhesive glycoprotein fibronectin, for the attachment and migration of corneal epithelial cells, and activation of these cells by biological agents such as the combination of substance P and insulin-like growth factor-1 (IGF-1). Central to both approaches is the role of the fibronectin-integrin system in corneal epithelial wound healing. Determination of the minimum amino acid sequences required for the promotion of corneal epithelial wound closure by fibronectin (PHSRN) and by substance P (FGLM-amide) plus IGF-1 (SSSR) has led to the development of peptide eyedrops for the treatment of PEDs that are free of adverse effects of the parent molecules.

Improving patient outcomes following glaucoma surgery: state of the art and future perspectives

Of all the treatments currently used to lower intraocular pressure in glaucoma patients, filtration surgery is known to be the most effective. However, in a significant percentage of cases, the constructed channel closes due to excessive scar formation, resulting in surgical failure. The process of postoperative wound healing is characterized by the coagulative and inflammatory phase, followed by the proliferative and repair phase, and finally the remodeling phase. Perioperative antimitotic agents, such as mitomycin C and 5-fluorouracil, are known to modulate the process of wound healing and to improve surgical outcome, but they carry a risk of vision-threatening complications. New alternative strategies to prevent filtration failure, such as inhibition of transforming growth factor-β, vascular endothelial growth factor, and placental growth factor, have shown promising results in the improvement of surgical success. However, it remains necessary to broaden the therapeutic approach by focusing on combined therapies and on extended drug delivery.

Distinct activation of epidermal growth factor receptor by UTP contributes to epithelial cell wound repair

The release of nucleotides after injury activates purinergic receptors, leading to phosphorylation of site-specific residues on epidermal growth factor receptor (EGFR). To elucidate the differences between the injury-induced response and that induced by exogenous EGF, we examined recruitment of docking proteins, internalization of EGFR, and migration after injury. Injury induced by scratch wounds or stimulation by addition of UTP caused a brief internalization of EGFR, which paralleled the lesser association with growth factor receptor-bound protein 2 (Grb2) and phosphorylation of EGFR. The internalization caused by EGF was sustained and detected for longer than 60 minutes and correlated with phosphorylation of the receptor. The EGF caused recruitment of Grb2, phospholipase C-γ-1 (PLCγ1), Shc, and Src to EGFR. Glutathione S-transferase pull downs were performed, and glutathione S-transferase-PLCγ1 showed binding of Grb2 when stimulated with EGF but not with UTP or injury. Furthermore, UTP did not induce PLCγ1 phosphorylation, and the phosphorylation induced by EGF was attenuated by costimulation with UTP. The response to heparin-binding EGF was equivalent to that of EGF. Site-directed mutagenesis showed that phosphorylation of Y1068 and Y1086 of EGFR is required for repair. Together, our results show that injury and activation of purinergic receptors and direct activation of EGFR via EGF induce distinct downstream pathways.

Corneal epithelial cell adhesion and growth on EGF-modified aminated PDMS

Growth factor tethering has significant potential to mediate cellular responses in biomaterials and tissue engineering. We have previously demonstrated that epidermal growth factor (EGF) can be tethered to polydimethylsiloxane (PDMS) substrates and that these surfaces promoted interactions with human corneal epithelial cells in vitro. The goal of the current work was to better understand the specific effects of the tethered growth factor on the cells. The EGF was reacted with a homobifunctional N-hydroxysuccinimide (NHS) polyethylene glycol (PEG) derivative, and then bound to allyamine plasma-modified PDMS. Human corneal epithelial cells were seeded on the surfaces and cultured in serum-free medium for periods of up to 5 days. Cell growth was monitored and quantified by trypsinization and counting with a Coulter counter. Expression of matrix proteins and alpha(6)-integrins was assessed by immunostaining and confocal microscopy. A centrifugation assay was used to determine cell adhesion under an applied detachment force. Binding of EGF was found to significantly increase cell numbers and coverage across the surfaces at 5 days of culture in vitro. Immunofluorescence experiments indicate increased expression of fibronectin, laminin, and alpha(6)-integrins on the EGF-modified surfaces, and expression is localized at the cell-material interface as observed by confocal microscopy. In accordance with these results, the highest quantity of adherent cells is found on the EGF-modified subtrates at 5 days of culture. The results provide initial evidence that binding of EGF may be used to improve the epithelialization of and the adhesion of the cells on a polymeric artificial cornea device.

Injury and nucleotides induce phosphorylation of epidermal growth factor receptor: MMP and HB-EGF dependent pathway

The early events that occur rapidly after injury trigger signal cascades that are essential for proper wound closure of corneal epithelial cells. We hypothesize that injury releases ATP, which stimulates purinergic receptors and elicits the phosphorylation of epidermal growth factor receptor (EGFR) tyrosine residues and subsequent cell migration by a MMP and HB-EGF dependent pathway. We demonstrated that the inhibition of purinergic receptors with the antagonist, Reactive Blue 2, abrogated the phosphorylation of EGFR and ERK. Pre-incubation of cells with the EGFR kinase inhibitor, AG1478, and subsequent stimulation by injury or ATP resulted in a decrease in phosphorylation of EGFR and migration. Furthermore, downregulation of EGFR by siRNA, inhibited the EGF-induced intracellular Ca(2+) wave. However, the response to injury and ATP was retained indicating the presence of two signaling pathways. Inhibition with either CRM197 or TIMP-3 decreased injury and nucleotide-induced phosphorylation of both EGFR and ERK. Incubation in the presence of a functional blocking antibody to HB-EGF also resulted in a decrease in the phosphorylation of EGFR. In addition, cell migration was inhibited by CRM197 and rescued when cells were incubated with HB-EGF. We showed that injury-induced phosphorylation of specific tyrosine residues and found that a similar pattern of phosphorylation was induced by trinucleotides. These studies indicate that injury-induced purinergic receptor activation leads to phosphorylation of EGFR, ERK and migration.

Correlation of proliferative and anti-apoptotic effects of HGF, insulin, IGF-1, IGF-2, and EGF in SV40-transformed human corneal epithelial cells

The effects of various growth factors on the proliferation and apoptosis of human corneal epithelial cells were investigated. Simian virus 40-transformed human corneal epithelial cells were thus incubated separately with eight different growth factors, after which cell proliferation was evaluated by measurement of [(3)H]thymidine incorporation or with the MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] assay and apoptosis was quantified by the terminal deoxyribonucleotidyl transferase-mediated dUTP-biotin nick-end labeling assay. Phosphorylation of the protein kinase Akt, which plays an important role in anti-apoptotic signaling, was also assessed by immunoblot analysis. The growth factors examined could be classified into three groups on the basis of their effects on the proliferation and apoptosis of human corneal epithelial cells: hepatocyte growth factor (HGF), insulin, insulin-like growth factor (IGF)-1, IGF-2, and epidermal growth factor (EGF) each increased cell proliferation, inhibited the induction of apoptosis by sodium nitroprusside, and elicited the activation of Akt; transforming growth factor-beta1 and -beta2 inhibited [3H]thymidine incorporation but had no effect on sodium nitroprusside-induced apoptosis or on Akt activity; and platelet-derived growth factor-BB had no effects on the measured parameters. HGF, insulin, IGF-1, IGF-2, and EGF may thus contribute to maintenance of the corneal epithelium and coordinate the proliferative and apoptotic responses of this tissue.

Topical therapeutic agents that modulate corneal wound healing

In summary, corneal wound healing is a complex phenomenon that involves interplay between the cellular elements of the cornea, numerous soluble factors, and the constituents of the ECM. Unfortunately, many studies that demonstrate marked alteration on cell behavior in vitro and even in in vivo experiments are often not helpful in the diseased patient, as shown by the results of careful clinical trials. Future work that addresses the complex milieu of the corneal wound healing environment by addressing the interaction of many of these factors will be more likely to be successful than seeking a single agent that will enhance wound healing in all situations. Modulation of wound healing processes by the application of topical therapeutic agents is, however, an expanding field of study sure to produce clinically significant improvements in the management of veterinary patients with corneal defects. The judicious use of topical cytoactive compounds has a place in the clinician's armamentarium integrated into a therapeutic plan that decreases the mechanical stresses imposed on the wound bed as well as removal of any underlying inciting cause.

Insulin, not leptin, promotes in vitro cell migration to heal monolayer wounds in human corneal epithelium

PURPOSE

To investigate the effects of insulin and leptin on in vitro wound healing of transformed human corneal epithelial cell monolayers and to identify cellular (migration versus proliferation) and intracellular signaling mechanisms.

METHODS

Scratch wounds were created in monolayers of an immortalized human corneal epithelial cell (HCEC) line. The wounded monolayers were exposed to insulin and leptin. Wound areas were measured every hour after wounding for up to 8 hours. Phosphoinositide 3-kinase (PI3-kinase) and mitogen-activated protein (MAP)-kinase signaling was analyzed with Western blot. The actions of insulin were also examined after incubation with inhibitors to extracellular signal regulated kinase (ERK 1/2) and PI3-kinase.

RESULTS

The presence of insulin, but not leptin facilitated closure of wounds created in corneal epithelial cell monolayers. Phosphorylation of ERK 1/2 and Akt was stimulated after exposure of the monolayers to insulin. Inhibitors of PI3-kinase and ERK 1/2 prevented or reduced insulin-induced corneal wound healing, respectively.

CONCLUSIONS

Exposure of corneal epithelium to insulin facilitated closure of in vitro small wounds through enhanced cell migration instead of proliferation, which depended on ERK 1/2 and PI3-kinase signaling. These data suggest a mechanism by which insulin may influence corneal wound healing in vitro. In vivo, disruptions to the insulin signaling pathway observed in diseases such as diabetes might account for the delayed wound healing and corneal defects.

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.

Connective tissue growth factor in tear film of the horse: detection, identification and origin

BACKGROUND

Healing of corneal ulcers in horses is often associated with profound corneal stromal fibrosis and scar formation resulting in visual impairment. Connective tissue growth factor (CTGF) is a fibrogenic cytokine involved in wound healing and scarring. The purpose of this study was to determine whether CTGF was present in the tear fluid of normal horse eyes and the eyes of horses with corneal ulcers in order to evaluate the role of CTGF in corneal wound healing and corneal scar formation.

METHODS

Tear fluid samples were collected from 65 eyes of 44 horses; 32 samples from normal eyes, 21 samples from eyes with corneal ulceration, and 12 samples from the unaffected contralateral eyes of horses with ulcers. CTGF levels in the tears were determined by enzyme immunoassay using goat IgG against human CTGF. Antigenetic similarity of human and horse CTGF was established in a bio-equivalence assay. The identity of horse CTGF was confirmed by western blot. Lacrimal and nictitating membrane glands were investigated by immunohistochemistry in the attempt to clarify the origin of tear fluid CTGF.

RESULTS

CTGF was detected in tear film of 23 normal unaffected eyes (72%) and 8 normal contralateral eyes (67%), with the mean CTGF levels (+/- SEM) being 51.5+/-19.2 and 13.4+/-3.9 ng/ml respectively. CTGF was found in 8 eyes with corneal ulcers (38%) with the mean CTGF concentration of 26.3+/-14.8 ng/ml. Western blot identified the protein detected as CTGF. The identification of CTGF in lacrimal glands suggests a major role of these glands in the presence of CTGF in tears.

CONCLUSIONS

CTGF is present in horse tear fluid and derives, at least partly, from the lacrimal gland. Equine CTGF has strong antigenic similarity with human CTGF. Corneal disease leads to a decrease of CTGF concentrations in tears. The possible role of CTGF in the healing process of ocular surface requires further investigation.

Interactions of corneal cells with transforming growth factor β2-modified poly dimethyl siloxane surfaces

The downgrowth of corneal epithelial cells at the interface of an artificial cornea and the host eye tissue poses a significant problem to be overcome in developing a successful implant. As a means of inhibiting the proliferation of corneal epithelial cells on the stromal surface of the implant, we examined the immobilization of transforming growth factor beta-2 (TGF-beta2) via a bifunctional poly ethylene glycol (PEG) spacer to poly dimethyl siloxane (PDMS) surfaces. Growth factor immobilization was confirmed by modification with (125)I-labeled TGF-beta 2. The modified surfaces were also characterized by advancing water contact angles, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Although the amount of growth factor covalently bound to the surface was difficult to quantify apparently due to strong interactions between the growth factor and the PEG layer and high levels of adsorption, differences in the modified surfaces, suggestive of the presence of a significant amount of TGF-beta 2, were found. In vitro interactions of the modified surfaces with human corneal epithelial and stromal cells were examined. Growth factor surface concentrations as well as culture in the absence and presence of serum and other adhesive proteins were examined. Corneal stromal and epithelial cells cultured on the TGF-beta 2-modified surfaces consistently gave results opposite to those expected. Likely, the most notable and surprising result was the almost complete lack of adhesion of the stromal cells, with coverage averaging between 3 and 5%. In comparison, corneal epithelial cell growth appeared to be promoted by the presence of the immobilized growth factor, with cell coverage averaging 50-60% at 7 days of culture. A TGF-beta 2 concentration effect was noted with both cell types in the absence of serum, with increases in the coverage at higher TGF-beta 2 concentrations. The observed cell growth appeared to be the result of interactions between the cells and active growth factor, because the addition of anti-TGF-beta 2 to the culture medium reduced cell coverage to levels similar to those noted on control surfaces. Therefore, although TGF-beta 2-modified surfaces may not be suitable as corneal epithelial cell inhibiting surfaces, interactions of surface immobilized growth factor and corneal cells are complex and should be further examined.

Growth factors but not gap junctions play a role in injury-induced Ca2+ waves in epithelial cells

This paper characterizes the early responses of epithelial cells to injury. Ca2+ is an important early messenger that transiently increases in the cytoplasm of cells in response to external stimuli. Its elevation leads to the regulation of signaling pathways responsible for the downstream events important for wound repair, such as cell migration and proliferation. Live cell imaging in combination with confocal laser scanning microscopy of fluo-3 AM loaded cells was performed. We found that mechanical injury in a confluent region of cells creates an elevation in Ca2+ that is immediately initiated at the wound edge and travels as a wave to neighboring cells, with [Ca2+]i returning to background levels within two minutes. Addition of epidermal growth factor (EGF), but not platelet-derived growth factor-BB, resulted in increased [Ca2+]i, and EGF specifically enhanced the amplitude and duration of the injury-induced Ca2+ wave. Propagation of the Ca2+ wave was dependent on intracellular Ca2+ stores, as was demonstrated using both thapsigargin and Ca2+ chelators (EGTA and BAPTA/AM). Injury-induced Ca2+ waves were not mediated via gap junctions, as the gap-junction inhibitors 1-heptanol and 18α-glycyrrhetinic acid did not alter wave propagation, nor did the cells recover in photobleaching experiments. Additional studies also demonstrated that the wave could propagate across an acellular region. The propagation of the injury-induced Ca2+ wave occurs via diffusion of an extracellular mediator, most probably via a nucleotide such as ATP or UTP, that is released upon cell damage.

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Effect of topical administration of epidermal growth factor on healing of corneal epithelial defects in horses

OBJECTIVE-To characterize healing of corneal epithelial defects in horses and to evaluate the ability of epidermal growth factor (EGF) to modulate rate of corneal epithelial healing in horses.

SAMPLE POPULATION

20 eyes in 12 adult horses.

PROCEDURE

Corneal epithelial wounds were created by mechanically debriding the limbus. Corneal healing was recorded for 3 treatment groups: 50 microg of EGF/ml (n = 5 eyes), 5 microg of EGF/ml (7), and PBS solution (8). Corneal healing was recorded once daily after instillation of fluorescein stain by use of photography and calculating the area of the wound, using imaging software.

RESULTS

After corneal debridement, re-epithelialization was rapid and progressed in a linear fashion for the first 5 to 7 days after surgery in all groups. After that period, rates of healing decreased. A profound increase in the degree of inflammation, neovascularization, melanosis, and scarring was observed in eyes treated with the high dose of EGF (50 microg/ml), but there was not a statistical difference in mean healing time or in mean decrease in radius during the linear phase between the control and either EGF treatment groups. However, for all 8 horses in which both eyes were debrided, the first eye healed significantly faster than the second eye, regardless of treatment.

CONCLUSIONS AND CLINICAL RELEVANCE

Beneficial effects of topical administration of a high dose of EGF for acceleration of healing of corneal defects in eyes of horses are outweighed by the intensity of the associated inflammatory response.

Tenascin and Cytokines in Tear Fluid After Photorefractive Keratectomy

BACKGROUND

Basic knowledge of the substances involved in wound healing after photorefractive keratectomy (PRK) is essential for development of pharmacological intervention. We present preoperative and postoperative analysis of tear fluid extracellular matrix proteins and cytokines after PRK.

METHODS

Tear fluid samples from 70 patients (72 eyes) who had PRK (38 women and 32 men, mean age 31.5 yr) were studied. Samples from 18 patients (18 eyes) were analyzed in two different studies.

RESULTS

Mean preoperative tear fluid flow in the collection capillary (volume divided by tear collection time) varied from 4.5 to 22.5 microliters/min in five series of patients. It increased significantly during the first two postoperative days (range of means, 55.5 to 88.8 microliters/min, p < 0.01), and decreased to the preoperative level by day 7 (range of means, 9.7 to 18.2 microliters/min). The tenascin and cytokine release rates increased significantly during the first two days after PRK and returned to the preoperative level by day 7. Mean +/- standard error for tenascin: day 0 (5.2 +/- 1.9 ng/min); day 2 (22.7 +/- 6.1 ng/min; p = 0.02). Mean +/- standard error for HGF: day 0 (3.2 +/- 0.7 pg/min); day 1 (22.8 +/- 4.2 pg/min; p = 0.0003). Mean +/- standard error for TGF-beta 1: day 0 (63.3 +/- 19.6 pg/min); days 1-2 (826.2 +/- 253.7 pg/min; p = 0.001). Mean +/- standard error for VEGF: day 0 (166.0 +/- 29.6 pg/min); days 1-2 (824.4 +/- 165.1 pg/min; p = 0.0007). Mean +/- standard error for PDGF-BB: day 0 (0.42 +/- 0.19 pg/min); day 2 (27.6 +/- 5.8 pg/min; p = 0.0000). Mean +/- standard error for TNF-alpha: day 0 (9.5 +/- 2.6 pg/min); day 2 (28.6 +/- 5.9 pg/min; p = 0.003). Excluding PDGF-BB, all substances studied were present in normal human tear fluid. PDGF-BB was present in only 17% of the preoperative samples.

CONCLUSION

Corneal wounding induces an increased release of several growth modulating cytokines which may be involved in healing processes.

Effects of hepatocyte growth factor, transforming growth factor-beta1 and epidermal growth factor on bovine corneal epithelial cells under epithelial-keratocyte interaction in reconstruction culture

In the cornea, corneal epithelial cells are in close contact with keratocytes: the epithelial cells organize thickened lamellar structure on a layer of keratocytes embedded in extracellular matrix (ECM). Thus, growth factors are expected to critically regulate corneal component cells under epithelial-keratocyte interaction. The purpose of this study is to clarify effects of hepatocyte growth factor (HGF), transforming growth factor-beta1 (TGF-beta1) or epidermal growth factor (EGF) on corneal epithelial cells under epithelial-keratocyte interaction. We examined proliferation and differentiation of the epithelial cells in a simple corneal reconstruction culture composed of an epithelial cell layer on the keratocyte-containing stromal layer, using three-dimensional collagen gel matrix culture. We observed the morphological change by phase contrast microscopy, and conducted histological and immunohistochemical examinations. The epithelial proliferation was examined by nuclear bromodeoxy-uridine (BrdU) uptake. In the reconstructed cornea under epithelial-keratocyte interaction, EGF-, TGF-beta1- and HGF-treated cells formed a thickened epithelial layer consisting of 5-6, 5-6 and 3-4 cells, respectively. In fact, both EGF and TGF-beta1 induced significantly higher intakes of nuclear BrdU of the epithelial cells than HGF. In lamellar differentiation of the epithelial cells, TGF-beta1- or HGF-treated cells formed a triple lamellar structure specific for the in vivo corneal epithelium: basal, middle and superficial layers are composed of cuboidal basal-like cells, spindle wing-like cells and flat superficial-like cells, respectively. TGF-beta1-treated cells formed a more markedly thickened epithelial layer than HGF-treated cells. In contrast, EGF formed a single lamellar structure consisting of cuboidal cells. These results suggest that those growth factors regulate proliferation and/or lamellar differentiation of corneal epithelial cells under epithelial-keratocyte interaction. The most interesting result was that TGF-beta1 promotes proliferation and lamellar differentiation of corneal epithelial cells through keratocyte-mediated stimulation.

TGF alpha can act as a chemoattractant to perioptic mesenchymal cells in developing mouse eyes

Growth factors are believed to play an important role in regulating cell fate and cell behavior during embryonic development. Transforming growth factor alpha (TGF alpha), a member of the epidermal growth factor (EGF) superfamily, is a small polypeptide growth factor. Upon binding to its receptor, the EGF receptor (EGFR), TGF alpha can exert diverse biological activities, such as induction of cell proliferation or differentiation. To explore the possibility that TGF alpha might regulate cell fate during murine eye development, we generated transgenic mice that express human TGF alpha in the lens under the control of the mouse alpha A-crystallin promoter. The transgenic mice displayed multiple eye defects, including corneal opacities, cataracts and microphthalmia. At early embryonic stages TGF alpha induced the perioptic mesenchymal cells to migrate abnormally into the eye and accumulate around the lens. In situ hybridization revealed that the EGFR mRNA is highly expressed in the perioptic mesenchyme, suggesting that the migratory response is mediated by receptor activation. In order to test this model, the TGF alpha transgenic mice were bred to EGFR mutant waved-2 (wa-2) mice. We found that the eye defects of the TGF alpha transgenic mice are significantly abated in the wa-2 homozygote background. Because the EGFR mutation in the wa-2 mice is located in the receptor kinase domain, this result indicates that the receptor tyrosine kinase activity is critical for signaling the migratory response. Taken together, our studies demonstrate that TGF alpha is capable of altering the migratory decisions and behavior of perioptic mesenchyme during eye development.

Modulation of intra-epithelial expansion of human T24 bladder-carcinoma cells in murine urothelium by growth factors and extracellular-matrix components

The high recurrence rate of bladder cancer is probably due to an efficient repopulation of the bladder by residual transformed cells after resection of the tumour. However, the regenerating capacity of the normal urothelial cells is very high. To study the balance between regenerating normal urothelium and out-growth of transformed urothelial cells, we recently developed an in vitro co-cultivation model. With this model system we studied the effects of growth factors and extracellular-matrix components on the intra-epithelial expansion of human T24 bladder-carcinoma cells in primary mouse-bladder explants. Exposure of the cultures to acidic fibroblast growth factor (aFGF) and laminin led to a dramatic increase in the number of invasive T24 cells into the primary urothelium. Epidermal growth factor (EGF) and collagen types I and IV counteracted the infiltration of individual T24 cells. EGF, aFGF, laminin and collagen types I and IV did not directly affect the migration and proliferation of T24 cells. Apparently, the efficacy of invasion of transformed urothelial cells into primary urothelium is not only dependent on the intrinsic characteristics of the transformed cells, but can be influenced to a considerable extent by exogenous components exerting their influence on the normal urothelium. The clinical relevance of this observation needs to be studied further.

An in vitro model of urothelial regeneration: effects of growth factors and extracellular matrix proteins

Although the cellular turnover of resting urothelium is very low, its regenerative capacity is known to be outstanding. In organotypic mouse urothelial cultures closely mimicking the differentiation and multilayering of normal urothelium, we examined the cell biological mechanisms underlying urothelial regeneration and the specific role of growth factors and several extracellular matrix (ECM) components. Exposure to epidermal growth factor (EGF) and acidic fibroblast growth factor (aFGF) and culture on laminin resulted in enhanced expansion of the urothelium. Microscopy and assessment of proliferative activity revealed that enhanced urothelial expansion due to EGF could be attributed to increased proliferative activity and an increase in cell numbers, whereas aFGF-stimulated expansion must be considered the consequence of increased cellularity and migration. Laminin-enhanced urothelial expansion was shown to be the result of spreading of the entire urothelial organotypic culture. This was associated with a considerable decrease in the number of cell layers. A synergistic effect of growth factors and laminin was not found. This organotypic urothelial cell culture model seems to be very useful in studying strategies to improve urothelial regeneration.

Growth factors and ocular wound healing

Protein growth factors regulate many of the processes in vitro that are essential for the process of normal ocular wound healing, including migration, mitosis and differentiation of cells. This has led to the hypothesis that peptide growth factors play key roles in regulating normal ocular wound healing in vivo. A corollary to this concept is that insufficient action of growth factors causes impaired healing, and prolonged action of growth factors produces excessive scarring. If both of these concepts are correct, then the addition of exogenous protein growth factors should enhance healing of chronic ocular wounds and reducing prolonged actions of growth factors should limit excessive scarring. Although much remains to be understood about the role of growth factors in ocular development and wound healing, results of a substantial number of laboratory and clinical experiments indicate that these hypotheses are generally correct. This article reviews the results of pre-clinical experiments and clinical trials investigating the roles of protein growth factors in ocular development and wound healing.

Growth factors in human tear fluid and in lacrimal glands

EGF has been shown to be a constant component of human tear fluid. Its concentration depends on the actual tear fluid flow, as shown for other proteins secreted by the lacrimal gland. This organ has also been considered to be the origin of tear fluid EGF and immunohistochemical evidence for this hypothesis was found. During corneal disease the concentration of EGF in tear fluid considerably decreases to levels even lower than those found during short time stimulation of reflex tearing. Other members of the EGF family, such as TGF-alpha, have considerable similarity with the EGF molecule and even bind to the same receptor. Currently it is thought that TGF-alpha may be, in certain phases of cell life, even more important in the regulation of cell metabolism than EGF. In the present study we have investigated the presence of TGF-alpha in tear fluid and the lacrimal gland. The initial results presented here, show for the first time that TGF-alpha like EGF, seems to be constant component of human tear fluid and to originate, at least partially, from the lacrimal gland.

Transforming growth factor-beta stimulates collagen and fibronectin synthesis by human corneal stromal fibroblasts in vitro

The effects of transforming growth factor-beta (TGF beta) and epidermal growth factor (EGF) on the synthesis of collagen and fibronectin, and on the proliferation of human corneal stromal fibroblasts in vitro, were evaluated. Human corneal stromal fibroblasts in culture were incubated for 48 hours with TGF beta or EGF in the absence of serum. Collagen and fibronectin in the culture media were measured by a collagenase-digestion assay and a competitive ELISA, respectively. The effects of the growth factors on proliferation were assessed by 3H-thymidine incorporation. Collagen synthesis was dose-dependently stimulated by TGF beta; at a concentration of 1 ng/ml of TGF beta, a 120% increase in collagen synthesis was seen over that of controls (p < 0.01). EGF, at a concentration of 10 ng/ml, induced a 40% increase in collagen synthesis over that of controls (p < 0.01). The maximum stimulation by TGF beta was greater than that by EGF (p < 0.05). Fibronectin synthesis was stimulated by TGF beta and EGF in a dose-dependent manner; 230% (p < 0.001) and 210% (p < 0.01) increases in fibronectin synthesis were caused by 10 ng/ml TGF beta and EGF, respectively. TGF beta and EGF dose-dependently stimulated 3H-thymidine incorporation. The maximum increases in 3H-thymidine incorporation reached 180% (p < 0.001) and 190% (p < 0.001) over that in controls, at 10 ng/ml concentrations of TGF beta and EGF, respectively. In conclusion, both TGF beta and EGF are potent stimulants of collagen and fibronectin synthesis and proliferation. Therefore, these two growth factors may be effective alternatives or additional choices for the treatment of corneal ulcer.

TGF alpha deficiency results in hair follicle and eye abnormalities in targeted and waved-1 mice

To explore the physiological roles of transforming growth factor alpha (TGF alpha), we disrupted the mouse gene by homologous recombination in embryonic stem cells. Homozygous mutant mice were viable and fertile, but displayed pronounced waviness of the whiskers and fur, accompanied by abnormal curvature, disorientation, and misalignment of the hair follicles. Homozygous and, to a lesser extent, heterozygous mice displayed eye abnormalities of variable incidence and severity, including open eyelids at birth, reduced eyeball size, and superficial opacity. Histological examination revealed eyelid and anterior segment dysgenesis, corneal inflammation and scarring, and lens and retinal defects. Although TGF alpha deficiency affected skin and eyes, wound healing in these tissues was not impaired. Similar hair and eye defects have been previously associated with the recessive mutation waved-1 (wa-1), and Northern analysis revealed reduced expression of TGF alpha in wa-1 mice. Crosses between wa-1 homozygotes and TGF alpha-targeted mice confirmed that wa-1 and TGF alpha are allelic.