Distribution of epidermal growth factor (EGF) receptors in rabbit corneal epithelial cells, keratocytes and endothelial cells, and the changes induced by transforming growth factor-beta 1

Blood-Based Treatments for Severe Dry Eye Disease: The Need of a Consensus

The use of blood-based eye drops as therapy for various diseases of the ocular surface has become increasingly popular in ophthalmic practice during recent years. The rationale for their use is based on the promotion of cellular proliferation and migration thanks to the supply of metabolically active substances, in particular growth factors. Blood-derived eye drops have been used for the treatment of several ocular surface disorders, such as dry eye disease, corneal ulcer, persistent epithelial defect, neurotrophic keratitis, ocular surface burn, recurrent corneal erosion, and limbal stem-cell deficiency. Both autologous (from patients themselves) and heterologous (from adult donors or from cord blood sampled at birth)-derived products exist, and each source has specific pros and cons. Despite an extensive literature, several issues are still under debate and the aim of this manuscript is to review the indications, preparation methods and storage, characterization of content, rationale for clinical outcomes, patient stratification, length of treatment, and rationale for repeated treatments at disease relapse. A rationale based on a "5 Ws and 2 Hs" protocol is proposed as a way of thinking, with the attempt to clarify Who, Why, When, Where, What, and How to use these treatment options.

Comparison of growth factor and interleukin content of adult peripheral blood and cord blood serum eye drops for cornea and ocular surface diseases

INTRODUCTION

Various blood-derived products have been proposed for the topical treatment of ocular surface diseases. The aim of the study was to compare the different content of Growth Factors (GFs) and Interleukins (ILs) in peripheral blood (PB-S) and Cord Blood (CB-S) sera.

MATERIALS AND METHODS

Sera were obtained from 105 healthy adult donors (PB-S) and 107 umbilical/placental veins at the time of delivery (CB-S). The levels of epithelial-GF (EGF), fibroblast-GF (FGF), platelet-derived-GF (PDGF), insulin-GF (IGF), transforming-GF alpha (TGF-α,) and beta 1-2-3 (TGF-β1-β2-β3), vascular endothelial-GF (VEGF), nerve-GF (NGF), Interleukin (IL)-1β,IL-4,IL-6,IL-10, and IL-13 were assessed by Bio-Plex Protein Array System (Bio-Rad Laboratories, CA, USA). The Mann-Whitney test for unpaired data was applied to compare GFs and ILs levels in the two sources. The associations among each GF/IL level and the obstetric data for CB-S and hematological characteristics for PB-S were also investigated.

RESULTS

The levels of EGF, TGF-α, TGF-β2, FGF, PDGF, VEGF, NGF, IL-1B, IL-4, IL-6, IL-10, and IL-13 were significantly higher in CB-S compared to PB-S. Conversely, the levels of IGF-1, IGF-2, and TGF-β1 were significantly higher in PB-S. The female sex and the weight of the child showed a significant association in predicting EGF and PDGF levels.

CONCLUSION

A significantly different content in those GFs and ILs was demonstrated in the two blood sources. Since each GF/IL selectively regulates different cellular processes involved in corneal healing, the use of PB-S or CB-S should be chosen on the basis of the cellular mechanism to be promoted in each clinical case.

Targeting growth factor supply in keratopathy treatment: comparison between maternal peripheral blood and cord blood as sources for the preparation of topical eye drops

BACKGROUND

Epitheliotrophic growth factors (GF) can be supplied topically to patients with severe keratopathy through a variety of blood-derived products. We compared GF content in adult peripheral blood serum (PB-S) and cord blood serum (CB-S) as potential sources of GF. To limit inter-individual variability the assessment was performed in maternal-child pairs at the time of delivery.

MATERIAL AND METHODS

The amounts of epidermal GF (EGF), insulin-like GF (IGF), transforming GF-beta (TGF-β), vascular endothelial GF (VEGF) in CB units collected from the umbilical vein and PB from mothers (each group n=30) were estimated by enzyme-linked immunosorbent assays. Obstetric characteristics and haematological data were recorded from the archives of the Emilia Romagna Cord Blood Bank. Statistical evaluations were performed by Wilcoxon's test and correlations between variables were determined using Spearman's (ρ) coefficient; p-values <0.05 were considered statistically significant.

RESULTS

EGF, TGF-β and VEGF levels were significantly higher in CB-S than in PB-S (median 1,254.4 vs 646.0 pg/mL, 51.3 vs 38.4 μg/mL and 686.8 vs 30 pg/mL, respectively; all p<0.0001) whereas IGF content was significantly higher in PB-S than in CB-S (159.9 vs 53.5 pg/mL, respectively; p<0.0001). In CB-S, the CD34(+) cell concentration appeared to be related to EGF, IGF and TGF-β levels whereas white blood cell count appeared to be related to EGF and TGF-β levels. VEGF levels showed no relation to the haematological parameters considered. Platelet counts were not related to GF level in either CB or PB.

DISCUSSION

The GF content in the two blood sources was different, with CB containing larger amounts. Each GF selectively regulates cellular processes involved in corneal healing, so the use of PB or CB should be targeted to supply specific GF on the basis of the type and severity of the keratopathy.

Effects of 17β-estradiol on human corneal wound healing in vitro

PURPOSE

To investigate the effect of 17β-estradiol on corneal wound healing, particularly on epithelial mitosis and migration.

METHODS

Immortalized human corneal epithelial cells (HCECs) were cultured in media with different concentrations of 17β-estradiol (10, 50, 100, and 200 pg/mL), Dulbecco modified Eagle medium: Nutrient Mixture F-12 (negative control), and serum-containing Dulbecco modified Eagle medium: Nutrient Mixture F-12 (positive control). After 6 or 24 hours of hormone treatment, to evaluate the migratory potential of 17β-estradiol, wound healing assays were conducted via the manual scraping of HCECs and western blot analysis of fibronectin and matrix metalloproteinase 9 (MMP9). The proliferative potential of 17β-estradiol was evaluated via a proliferation assay using western blot analysis for proliferating cell nuclear antigen. In addition, epidermal growth factor (EGF) was measured by reverse transcription-polymerase chain reaction, and for the inhibition of epidermal growth factor receptor (EGFR)-mediated signal transduction, a wound healing assay was conducted after HCECs cultured with EGFR small interfering RNA were stimulated with 100 pg/mL 17β-estradiol.

RESULTS

Wound healing assay rates were enhanced as 17β-estradiol increased, with statistically significant changes seen in 50, 100, and 200 pg/mL 17β-estradiol-treated and positive control cells, compared with negative control cells (P < 0.05, in each group). Western blot analysis revealed that the expression of the MMP9 gene was upregulated by 17β-estradiol, and the expression of the fibronectin gene was downregulated by 17β-estradiol. The mitosis assay via western blot analysis showed that the expression cell cycle-associated protein, proliferating cell nuclear antigen, increased gradually as a result of 17β-estradiol treatment. Reverse transcription-polymerase chain reaction showed that EGF was upregulated by 17β-estradiol, and the EGFR small interfering RNA did not totally block the wound healing of the 17β-estradiol-treated cells but statistically significantly reduced the wound healing rate (P = 0.031).

CONCLUSIONS

17β-Estradiol facilitated the maintenance of the beneficial effect on corneal epithelial migration and proliferation, and the promoting effect of 17β-estradiol is partially related to increased EGF in vitro.

New therapeutic approaches in the treatment of diabetic keratopathy: a review

The cornea is densely innervated, and the integrity of these nerve fibres is critical in maintaining the refractive and protective functions of the cornea. Many ocular and systemic diseases can adversely affect corneal sensory nerves and consequently impair their function, with vision loss being the inevitable consequence of severe corneal neurotrophic ulceration. However, current standard treatments regimens are often ineffective. Over the past three decades, the role of growth factors in maintaining the normal structure and function of the cornea, and in corneal epithelial healing, has become increasingly evident. Many preclinical and clinical trials have shown that growth factors and cytokines can significantly enhance epithelialization (epithelial proliferation and migration) and consequently accelerate wound healing. More recently, local/topical administration of insulin, naltrexone (opioid antagonist) and nicergoline (ergoline derivatives) were found to improve, and significantly increase, the corneal wound healing rate. This report reviews the major attributes of these growth factors and therapeutic agents that may be used in ameliorating impaired corneal wound healing, and presents a perspective on the potential clinical use of these agents as a new generation of ophthalmic pharmaceuticals for the treatment of diabetic keratopathy.

Growth factors and corneal epithelial wound healing

In this article, we briefly review recent findings in the effects of growth factors including the EGF family, KGF, HGF, IGF, insulin, and TGF-beta on corneal epithelial wound healing. We discuss the essential role of EGFR in inter-receptor cross-talk in response to wounding in corneal epithelium and bring forward a concept of "alarmins" to the field of wound healing research.

Epidermal growth factor synergism with TGF-beta1 via PI-3 kinase activity in corneal keratocyte differentiation

PURPOSE

To investigate the action of epidermal growth factor (EGF) on corneal keratocyte differentiation and its effects in conjunction with transforming growth factor (TGF)-beta1.

METHODS

Rabbit corneal keratocytes (RCKs) were treated with EGF, TGF-beta1, or EGF plus TGF-beta1 in the presence or absence of inhibitors of EGF-receptor (EGF-R), neutralizing concentrations of EGF antibody and of signaling kinases for 2 days to 1 week. RCK differentiation to myofibroblasts was identified with anti-aldehyde dehydrogenase (ALDH)-1 and alpha-smooth muscle actin (alpha-SMA) antibodies. Cell proliferation was evaluated with anti-Ki-67 antibody. Extracellular matrix (ECM) components were assayed by immunochemistry and Western blot. Cell migration images were captured with a camera attached to the microscope, and the area of the wound was calculated using imaging software.

RESULTS

RCKs cultured in serum-free DMEM/F12 without frequent changes of medium maintained the phenotype for more than 1 month. EGF stimulated differentiation into a proto-myofibroblast phenotype with the loss of dendritic shape and the expression of alpha-SMA. Treatment with TGF-beta1 stimulated 12% of the cells to differentiate to defined myofibroblasts, but in the presence of EGF, TGF-beta1 induced 90% of RCKs to transform into myofibroblasts. Inhibition of EGF-R activation and of the phosphatidylinositol-3 kinase (PI-3K)/Akt-1 pathway prevented the action of EGF on TGF-beta1 cell differentiation. TGF-beta1 in the presence of EGF also increased cell migration, which is inhibited by blocking EGF-R activation.

CONCLUSIONS

These data show that EGF contributes to the differentiation and migration of myofibroblasts induced by TGF-beta1 through EGF-R activation and that it is an important modulator of wound healing and scar tissue formation.

Growth Factors in the Tear Film: Role in Tissue Maintenance, Wound Healing, and Ocular Pathology

Numerous biologically active growth factors are secreted by the lacrimal gland and distributed via the tears over the ocular surface, where they affect cellular proliferation, migration, differentiation, and survival. The role of growth factors and their receptors in maintenance of tissue homeostasis and wound healing continues to be elucidated, and the effect of growth factor imbalances in ocular surface diseases is just beginning to be understood. For instance, in eyes with ocular surface diseases, including conjunctivitis, corneal erosion, keratitis, and corneal ulcers, epidermal growth factor release rates have been shown to be significantly lower than in normal eyes during reflex tearing. Future research into the mechanisms of dry eye disease will focus on reasons for decreased tear and growth factor production in the neuronal reflex loop or the acinar lacrimal gland cells. Animal models to test therapeutic approaches must be developed.

EGF-grafted PDMS surfaces in artificial cornea applications

Lack of epithelial cell coverage has remained a persistent problem in the design of an artificial cornea. In this work, polydimethylsiloxane (PDMS) surfaces were modified with epidermal growth factor (EGF) to improve the growth of corneal epithelial cells. The EGF was covalently tethered to PDMS substrates aminated by plasma polymerization of allylamine via a homobifunctional polyethylene glycol (PEG) spacer. Surface modification was confirmed by contact angle and X-ray photoelectron spectroscopy measurements. By varying the ratio of EGF to PEG from 1:50 to 1:5, EGF amounts from 40 to 90 ng/cm2 could be bound, as determined by surface plasmon resonance (SPR) and 125I radiolabelling. Human corneal epithelial cells on the various modified surfaces were cultured both in the presence and absence of EGF in the culture medium to determine the effect of covalently bound EGF on the cells. The results demonstrated that covalently bound EGF on the surfaces is active with respect to promoting epithelial cell coverage. This was significant when compared to unmodified controls.

Growth factors in the anterior segment: role in tissue maintenance, wound healing and ocular pathology

A number of growth factors and their associated receptors, including epidermal growth factor, transforming growth factor-beta, keratinocyte growth factor, hepatocyte growth factor, fibroblast growth factor and platelet-derived growth factor have been detected in the anterior segment of the eye. On binding to cellular receptors, these factors activate signalling cascades, which regulate functions including mitosis, differentiation, motility and apoptosis. Production of growth factors by corneal cells and their presence in the tear fluid and aqueous humour is essential for maintenance and renewal of normal tissue in the anterior eye and the prevention of undesirable immune or angiogenic reactions. Growth factors also play a vital role in corneal wound healing, mediating the proliferation of epithelial and stromal tissue and affecting the remodelling of the extracellular matrix (ECM). These functions depend on a complex interplay between growth factors of different types, the ECM, and regulatory mechanisms of the affected cells. Imbalances may lead to deficient wound healing and various ocular pathologies, including edema, neovascularization and glaucoma. Growth factors may be targeted in therapeutic ophthalmic applications, through exogenous application or selective inhibition, and may be used to elicit specific cellular responses to ophthalmic materials. A thorough understanding of the mechanism and function of growth factors and their actions in the complex environment of the anterior eye is required for these purposes. Growth factors, their function and mechanisms of action as well as the interplay between different growth factors based on recent in vitro and in vivo studies are presented.

Effects of growth factors (EGF, PDGF-BB and TGF-beta 1) on cultured equine epithelial cells and keratocytes: implications for wound healing

OBJECTIVE

The physiologic mechanisms involving growth factors, including PDGF-BB, EGF, and TGF-beta 1, as potent mediators of fibroblasts and epithelial cells in corneal wound healing remain unknown. The goal of this study was to determine culture methods for equine epithelial cells and keratocytes and to investigate how exogenous growth factors influence proliferation of both cell types.

PROCEDURES

Cell cultures were established from healthy corneas harvested from horses immediately following euthanasia and maintained using standard tissue culture protocols. To determine the effects of PDGF-BB, EGF, TGF-beta 1, keratocytes (1 x 10(5)/well) and epithelial cells (2 x 10(5)/well) were each cultured in 12 well plates and exposed separately to the growth factors. The cells were exposed to concentrations of EGF between 0 and 50 ng/mL; PDGF-BB between 0 and 75 ng/mL; and TGF-beta 1 between 0 and 10 ng/mL. Cell proliferation was measured using 3H-thymidine assay and differences in growth determined using anova and Tukey's HSD test (P < 0.05).

RESULTS

Epithelial cell and keratocyte cultures were successfully established. EGF maximally stimulated keratocyte and epithelial cells at 25 ng/mL and 5 ng/mL, respectively. PDGF-BB maximally stimulated keratocytes and epithelial cells at 50 ng/mL and 5 ng/mL, respectively. TGF-beta 1 inhibited keratocytes at 5 ng/mL and 10 ng/mL, and epithelial cells at 1 ng/mL and 2 ng/mL.

CONCLUSIONS

Methods were established to maintain epithelial cells and keratocytes in vitro. PDGF-BB and EGF stimulate, while TGF-beta 1 inhibits the proliferation of epithelial cells and keratocytes. These growth factors may play a role in maintenance and repair of the equine cornea.

Transporters/receptors in the anterior chamber: pathways to explore ocular drug delivery strategies

Membrane transporters/receptors are involved in drug transport processes and play a key role in intestinal absorption, tissue distribution and elimination. Drug targeting to specific transporters and receptors using carrier-mediated absorption has immense clinical significance. Ocular drug delivery is a challenging task since it involves drug transport across various barriers in the eye. Specialised transport processes exist at these barriers, which control the entry of drugs and xenobiotics. Ocular drug therapy involving topical or systemic administration of drugs has various limitations. Transport processes in the eye have been targeted in an effort to increase ocular bioavailability of drugs following topical instillation. This review discusses various transport processes in the eye and drug delivery strategies utilising these transporters/receptors.

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.

Pterygial derived fibroblasts express functionally active histamine and epidermal growth factor receptors

Pterygia are characterised by a fleshy outgrowth of altered conjunctival tissue over the cornea and are most common in tropical regions. Pterygial fibroblasts are characteristically distinct from normal conjunctival fibroblasts, and therefore the aim of this study was to determine the presence and functional significance of histamine and epidermal growth factor (EGF) receptors in these cells. Pterygial specimens were cultured in vitro and cellular outgrowths were phenotypically characterised as fibroblasts using vimentin and cytokeratin staining. Intracellular calcium mobilization was used to characterise the functional activity of histamine receptors on these cells. Maximal response was obtained with 100 microM histamine. However, lower concentrations of histamine also caused mobilization of calcium that were totally abolished by pre-incubation with H1 but not H2 or H3 receptor antagonists. EGF receptor was diffusely expressed over the cell surfaces. EGF stimulated receptor internalization, ERK protein phosphorylation and intracellular calcium mobilization. Therefore, fibroblasts derived from human pterygia express functionally active histamine and epidermal growth factor receptors. Controlled modification of either the receptors or the appropriate ligands could have beneficial effects in pterygia treatment.

Altered expression of growth factors and cytokines in keratoconus, bullous keratopathy and diabetic human corneas

The purpose of this study was to identify the growth factors and cytokines present in normal and diseased corneas. Total RNA was isolated from normal and diseased corneas. cDNA was synthesized from individual corneas and semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) was performed with primers to IL-1alpha, 1IL-8, PDGF-B, BMP-2, BMP-4, IGF-I, TGF-beta2, FGF-2, and VEGF. After normalization to beta2-microglobulin, several factors were identified that were significantly different from normal. Antibodies to IGF-I, BMP-2, VEGF and TGF-beta2 were used for immunohistochemistry. A total of 93 corneas were used for this study including 31 normal, 20 keratoconus, 19 bullous keratopathy (pseudophakic and aphakic, PBK/ABK), and 23 diabetic corneas. The VEGF RNA levels were significantly decreased in the keratoconus and PBK/ABK corneas but increased in the diabetic corneas. BMP-2 gene expression was lower than normal in the PBK/ABK and diabetic corneas. IGF-I and BMP-4 RNA levels were increased in PBK/ABK. In the immunohistochemical studies, the protein patterns paralleled those found at the mRNA level. The only exception was IGF-I in diabetic corneas that showed increased staining in the epithelium and its basement membrane without a significant increase in mRNA levels. TGF-beta2 mRNA and protein levels were similar to normal in all diseased corneas. Thus, no alterations in the tested growth factors/cytokines were unique to keratoconus corneas. In contrast, PBK/ABK corneas had specific significant elevations of BMP-4 and IGF-I. Diabetic corneas were unique in their increased VEGF mRNA levels. These data suggest that while some growth factor/cytokine alterations are non-specific and can be found in multiple corneal diseases, there are others that are unique to that disease.

Optimal concentration of human epidermal growth factor (hEGF) for epithelial healing in experimental corneal alkali wounds

PURPOSE

By using both in vivo and in vitro (organ-cultured) systems, the optimal concentrations of hEGF to enhance epithelial healing after alkali wounds were evaluated in the rabbit cornea.

METHODS

Alkali-injured corneas (pi = 5.5 mm, 1 N NaOH, 60 s) were treated with 0.01, 0.1, 1.0, 10 and 100 ng/ml hEGF for the in vitro study. The healing of epithelium and endothelium was determined at 1, 2, 3, 4, and 6 days after treatment. For the in vivo experiment, the eyes were treated with 2, 5, 10, and 50 microg/ml hEGF 3 times per day. The measurement of epithelial healing rate, transmission electron microscopy and immunohistochemical observation were performed after 7 days treatment.

RESULTS

In in vitro tests, hEGF enhanced the epithelial healing rates, showing a maximum enhancement at the concentration of 1.0 ng/ml, and endothelial healing was increased at 100 ng/ml. In in vivo studies, no significant difference was observed in the rates of epithelial healing between control and each hEGF-treated group. Among the tested concentrations, 5 microg/ml hEGF induced the most active proliferation of basal cells and 50 microg/ml hEGF remarkably produced a vascular ingrowth to the central wound area. The thickness of re-surfaced epithelium was increased by hEGF in a concentration-dependent manner.

CONCLUSIONS

The results of the present study indicate that a low concentration of hEGF may selectively enhance epithelial healing without affecting endothelial healing. The optimal concentration of hEGF for the stimulation of epithelial healing appears to be 5 microg/ml in rabbit corneal alkali wounds.

Expression of the receptor tyrosine kinases, epidermal growth factor receptor, ErbB2, and ErbB3, in human ocular surface epithelia

PURPOSE

To investigate the distribution and relative level of expression of the receptor tyrosine kinases, epidermal growth factor receptor (EGFR), ErbB2 and ErbB3, in human ocular surface epithelia.

METHODS

Immunofluorescent staining was performed to identify expression of the EGFR, ErbB2 and ErbB3 in the corneal, limbal and conjunctival epithelium in tissue sections and impression cytologies taken from normal human eyes. Western blotting was undertaken to confirm the results of immunofluorescent staining.

RESULTS

The three receptor tyrosine kinases, EGFR, ErbB2 and ErbB3, were detected in human corneal, limbal and conjunctival epithelia by immunofluorescent staining. Strong staining for the EGFR was observed in the basal epithelial cells at all 3 sites and throughout the corneal epithelium. Minimal or no staining for the EGFR was observed in the superficial conjunctival and limbal epithelia. The strongest staining for ErbB2 and ErbB3 was observed in the superficial ocular surface epithelium. All three receptors were detected in the corneal, limbal and conjunctival epithelium by western blot.

CONCLUSION

EGFR, ErbB2 and ErbB3 are expressed by the ocular surface epithelia. EGFR is preferentially expressed by the basal epithelial cells that have the greatest proliferative potential. In contrast, ErbB2 and ErbB3 are preferentially expressed by the superficial differentiated ocular surface epithelia.

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.

Increased expression of the type 1 growth factor receptor family in the conjunctival epithelium of patients with keratoconjunctivitis sicca

PURPOSE

To investigate the expression of type 1 growth factor receptors (epidermal growth factor receptor, ErbB2, and ErbB3) in the conjunctival epithelium of patients with keratoconjunctivitis sicca.

METHODS

Immunofluorescent staining and Western blotting were performed to grade the level of expression of the epidermal growth factor receptor ErbB2, and ErbB3 in conjunctival epithelial impression cytologies taken from both eyes of seven normal subjects and 22 patients with keratoconjunctivitis sicca.

RESULTS

Epidermal growth factor receptor staining was observed in a greater percentage of keratoconjunctivitis sicca than normal samples (P <.05). ErbB2 and ErB3 staining in the apical conjunctival epithelium was observed in both groups, but stronger ErbB2 and ErbB3 staining was noted in keratoconjunctivitis sicca conjunctival samples (P <.05). The relative levels of expression of these receptor proteins on immunoblots were consistent with immunofluorescent staining. On immunoblots, epidermal growth factor receptor protein was detected in 50% of keratoconjunctivitis sicca samples, but none of the normal samples (P <.025). The expression of ErbB2 and ErbB3 on immunoblots was also greater in the keratoconjunctivitis sicca samples (P <.05). Immunofluorescent staining scores for these receptors were correlated with conjunctival lissamine green staining scores (r =. 574, P <.01 for epidermal growth factor receptor; r =.620, P <.0025 for ErbB2; r =.502, P <.025 for ErbB3) and with corneal fluorescein staining (r =.409, P <.05 for ErbB2; r =.588, P <.005 for ErbB3).

CONCLUSION

The expression of the type 1 growth factor receptors is significantly greater in the conjunctival epithelium of eyes with keratoconjunctivitis sicca than normal eyes. The increased expression of these receptors was positively correlated with ocular surface dye staining. The increased expression of these receptors may contribute to the abnormal growth and differentiation of the conjunctival epithelium that occurs in keratoconjunctivitis sicca.

Growth factors: importance in wound healing and maintenance of transparency of the cornea

The mechanism of corneal wound healing has not been clarified yet. However, evidence has accumulated that various kinds of growth factor such as epidermal growth factor (EGF), fibroblast growth factor (FGF), transforming growth factor (TGF), keratinocyte growth factor (KGF), hepatocyte growth factor (HGF), platelet-derived growth factor (PDGF) and insulin-like growth factor (IGF) play a key role in corneal wound healing. For example, these growth factors are expressed in the corneal epithelial cells, keratocytes and endothelial cells, and their receptors are expressed in the corneal cells. Furthermore, these growth factors promote the proliferation of corneal cells and induce the migration of corneal cells. In addition to the growth factors, inflammatory cytokines such as interleukin (IL)-1, IL-6 and TNF-alpha are involved in corneal wound healing. These cytokines are expressed in the normal and inflammatory cornea after infections, alkaliburn, etc. where they control the growth of corneal cells and induce the migration of corneal cells. Thus, a number of growth factors and cytokines function in the regulation of corneal cell proliferation and in the maintenance of corneal transparency.

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.

The effects of growth factors and conditioned media on the proliferation of human corneal epithelial cells and keratocytes

BACKGROUND

As growth factors play an important role in epithelial wound repair, we evaluated the effect of exogenous growth factors in the presence and absence of corneal epithelial and keratocyte conditioned medium on human corneal epithelial cell and keratocyte proliferation.

METHODS

Preconfluent cultures of human corneal epithelial cells or stromal keratocytes were exposed to varying concentrations of EGF, TGF-beta or bFGF in the presence or absence of human corneal epithelial or stromal keratocyte conditioned medium. Cell numbers were determined after 48 h incubation. RIA and ELISA were used to quantify the levels of EGF, TGF-beta and bFGF in conditioned media.

RESULTS

EGF and bFGF increased, while TGF-beta decreased, the proliferation of both cell types in a dose-dependent manner. Epithelial cell conditioned medium inhibited, and keratocyte conditioned medium stimulated, the proliferation of both cell types. The proliferative effects of EGF, TGF-beta and bFGF in the presence of keratocyte conditioned medium were additive for both cell types. By contrast, the addition of exogenous growth factors was unable to overcome the inhibitory potential of epithelial conditioned medium. Both conditioned media contained significant levels of bFGF, but TGF-beta levels in epithelial conditioned medium were up to 5 times greater than that in keratocyte conditioned medium.

CONCLUSIONS

The results indicate that corneal cells maintain tissue homeostasis and modulate the wound healing response via paracrine/autocrine pathways.

Epidermal growth factor (EGF) receptor density controls mitogenic activation of normal rat kidney (NRK) cells by EGF

Normal rat kidney (NRK) fibroblasts are immortalized cells that are strictly dependent on externally added growth factors for proliferation. When cultured in the presence of epidermal growth factor (EGF) as the only growth stimulating hormone, these cells have a normal phenotype and undergo density-dependent growth inhibition. It has been postulated that this density-arrest results from a decrease of EGF receptor levels below a threshold level which makes these cells unresponsive to stimulation by EGF. In the present study, we show that NRK cells, made quiescent by serum-deprivation at submaximum density, are mitogenically still responsive to EGF, but show enhanced mitogenic stimulation after 8 hr pre-treatment with either transforming growth factor beta (TGF beta) or retinoic acid (RA), while prostaglandin F2 alpha (PGF2 alpha) and bradykinin (BK) enhance the mitogenic stimulation by EGF only slightly under these conditions. Addition of TGF beta or RA results in an increase of both 125I-EGF-binding capacity and EGF receptor mRNA levels. Using flow cytometric analysis, we show that pre-treatment with TGF beta or RA increases the percentage of cells entering the cell cycle as a function of time. Furthermore, pre-treatment of the cells with TGF beta or RA increases the rate of mitogen-activated protein kinase (MAPK) phosphorylation by EGF. PGF2 alpha and BK also increase EGF receptor levels, but only with delayed kinetics. These results show that already in serum-deprived quiescent NRK cells, EGF receptor levels limit EGF-induced mitogenic stimulation. This observation provides further evidence for the regulating role of the EGF receptor in density-dependent growth control of NRK cells.

Effect of transforming growth factor-beta1 and -beta2 on in vitro rabbit corneal epithelial cell proliferation promoted by epidermal growth factor, keratinocyte growth factor, or hepatocyte growth factor

Corneal epithelial wound healing is intimately controlled by a variety of growth factors, such as epidermal growth factor (EGF), keratinocyte growth factor (KGF), hepatocyte growth factor (HGF), and transforming growth factor-betas (TGF-betas). In this study, we investigate the effects of TGF-beta1 and TGF-beta2 on cultured rabbit corneal epithelial cell proliferation promoted by EGF, KGF, or HGF. Both TGF-beta1 and -beta2 dose-dependently inhibited corneal epithelial cell proliferation promoted by KGF (40 ng ml-1) and HGF (40 ng ml-1), and weakly inhibited cell proliferation promoted by EGF (4 ng ml-1). Furthermore, the inhibitory effect tended to be stronger with TGF-beta2 than TGF-beta1. These findings suggest that TGF-beta1 and -beta2 play important roles as negative modulators against the cell proliferation effect of EGF, KGF and HGF.

Corneal endothelium and growth factors

Human corneal endothelium is characterized by a low regenerative capacity, mainly because of a low mitotic activity, and therefore complete regeneration of the endothelial layer after injury is precluded. A decrease in endothelial cell density and an abnormal cell mosaic, which may occur after many conditions, can compromise the integrity of the endothelial monolayer, resulting in corneal decompensation with reduced vision and eventual need for penetrating keratoplasty. It would be beneficial to have growth factors that can help to maintain or restore the integrity of this delicate endothelial monolayer by maintaining or increasing the endothelial cell density or to stimulate the regeneration during wound healing. Growth factors represent a group of signalling peptides which influence diverse cellular processes, including cell proliferation, differentiation, migration and survival. One of the areas that has received great interest is its enhancement of wound healing. In this review the effects of three most effective growth factors (EGF, PDGF, FGF) on corneal endothelium, especially on wound healing in human corneal buttons, will be discussed.

Orientation and directed migration of cultured corneal epithelial cells in small electric fields are serum dependent

Reorientation and migration of cultured bovine corneal epithelial cells (CECs) in an electric field were studied. Electric field application was designed to model the laterally directed, steady direct current electric fields which arise in an injured corneal epithelium. Single cells cultured in media containing 10% foetal bovine serum showed significant galvanotropism, reorienting to lie perpendicular to electric field vector with a threshold field strength of less than 100 mV/mm. Cells cultured in serum-free medium showed no reorientation until 250 mV/mm. Addition of EGF, bFGF or TGF-beta 1 singly or in combination to serum free medium significantly restored the reorientation response at low field strengths. Both the mean translocation rate and directedness of cell migration were serum dependent. Cultured in medium with serum or serum plus added EGF, single cells showed obvious cathodal migration at 100 mV/mm. Increasing electric field strength enhanced the cathodal directedness of single cell migration. Supplementing serum free medium with growth factors restored the cathodal directed migration of single cells and highest directedness was found for the combination of EGF and TGF-beta 1. Corneal epithelial sheets also migrated towards the cathode in electric fields. Serum or individual growth factors stimulated CEC motility (randomly directed). Applied fields did not further augment migration rates but added a vector to stimulated migration. Electric fields which are present in wounded cornea interact with other environmental factors and may impinge on CECs migration during wound healing. Therapies which combine the application of growth factors and electric fields may be useful clinically.

IGF-I and EGF receptors in the pigmented rabbit bulbar conjunctiva

The purpose of this study was to investigate whether receptors for insulin-like growth factors I and II (IGF-I and IGF-II), insulin, epidermal growth factor (EGF), and transforming growth factor alpha (TGF alpha) are present on the apical surface of the pigmented rabbit bulbar conjunctiva. Binding of 125I-labelled ligands to the apical surface of the pigmented rabbit bulbar conjunctiva was conducted at 4 degrees C in the absence and presence of excess unlabeled ligands. There was no evidence for the existence of IGF-II, insulin or TGF alpha receptors in the isolated pigmented bulbar conjunctiva. Only IGF-I and EGF receptors appeared to be present. The apparent dissociation constant (Kd) of IGF-I receptors was 206 +/- 13 pM and that for EGF was 51 +/- 5 pM. The number of receptors per 95 mm2 of bulbar conjunctiva was (6.0 +/- 0.2)X10(9) for IGF-I and (2.4 +/- 0.1)X10(9) for EGF. There was no crossover binding of either IGF-I or EGF to one another's receptors. The IC50 value for competitive displacement of bound 125I-IGF-I was: 44 +/- 2 nM by IGF-I, 156 +/- 13 nM by IGF-II and 812 +/- 78 nM by insulin. The IC50 value for displacement of bound 125I-EGF was 0.37 +/- 0.03 nM by EGF and 0.42 +/- 0.04 nM by TGF alpha. In conclusion, only IGF-I and EGF receptors appear to be present on the apical surface of the pigmented rabbit bulbar conjunctiva. The IGF-I receptor is also capable of binding IGF-II and insulin, whereas the EGF receptor is also capable of binding TGF alpha.

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.

Regional variation in distribution of EGF receptor in developing and adult corneal epithelium

Epidermal growth factor receptor has been localized to the proliferative cell layers in a variety of stratified squamous epithelia. In the current study, the rat cornea was used as an experimental model to determine if epidermal growth factor receptor is concentrated in epithelial stem cells. Epidermal growth factor receptor was localized using immunofluorescence microscopy in adult and neonatal (1-day to 4-week) rat corneas. Antibody binding to epidermal growth factor receptor was present in basal cells across the adult cornea but was more intense in the limbal zone. In rats 1 day to 1 week of age, the corneal epithelium consisted of one or two layer of cells that were intensely labeled by anti-epidermal growth factor receptor. Following epithelial stratification, which occurred just prior to eyelid opening (approximately 12 days), expression of epidermal growth factor receptor was greatly reduced in central corneal epithelium and gained an adult pattern by 3 weeks of age. Expression of epidermal growth factor receptor was also examined by incubating 1 mm slices of adult corneas with 125I-epidermal growth factor (4 nM) for 90 minutes, followed by washing and autoradiography. Basal cells in the limbal zone contained 4.5-fold more silver grains per cell than did basal cells in the central cornea. These data suggest that cells with high potential for proliferation, i.e. limbal basal cells and all basal cells in developing rats, express high epidermal growth factor receptor levels. High levels of receptor may allow these cells to be rapidly stimulated by growth factors to undergo cell division during development and following wounding in adult corneas.(ABSTRACT TRUNCATED AT 250 WORDS)

Transforming growth factor-beta modulates effects of epidermal growth factor on corneal epithelial cells

In order to understand the mechanisms that bring about maintenance and restoration of the integrity of corneal epithelium, we investigated independent and combined effects of transforming growth factor-beta (TGF-beta) and epidermal growth factor (EGF) on rabbit corneal epithelial cells in cell and organ culture. Specifically, we determined whether incubation with these factors influenced 1) cellular proliferation, 2) ability of cells to attach to a fibronectin matrix, and 3) the rate of epithelial migration over corneal stroma. Incubation with TGF-beta caused a dose-related decrease in the incorporation of 3H-thymidine by the epithelial cells. EGF increased 3H-thymidine incorporation, but this effect was antagonized by the addition of TGF-beta into the incubation medium. Incubation with EGF increased the numbers of cells that attached to a fibronectin matrix. TGF-beta itself did not affect the number of attached cells but, again, it antagonized the stimulatory effect of EGF. Similarly, when corneal blocks were cultured with EGF, epithelial migration increased in a dose-related manner. TGF-beta itself did not affect epithelial migration at any of the concentrations tested (0.1-10 ng/ml), but it antagonized EGF-stimulated epithelial migration. These findings suggest that the proliferation and the migration of corneal epithelial cells are regulated by different mechanisms, and that TGF-beta serves as a modulator of the effects of EGF.