Interference of sympathetic overactivation restores limbal stem/progenitor cells function and accelerates corneal epithelial wound healing in diabetic mice

Diabetic keratopathy (DK), the diabetic complication in the cornea, is characterized by the delayed epithelial regeneration and sensory nerve degeneration. The involvement of limbal stem/progenitor cells (LSPCs) dysfunction has been reported, however the pathogenic mechanisms remain unclear. Here, we confirmed the dysfunction of LSPCs in diabetic mouse and human corneas. The sympathetic nerve in the cornea was adjacent to LSPCs, and the sympathetic overactivation was found in diabetic mice. Surgical and pharmacological ablation of sympathetic nerves rescued the LSPCs function and promoted corneal epithelial regeneration in diabetic mice. In contrast, both topical norepinephrine (NE) application and chemogenetic sympathetic overactivation directly impaired the stemness and proliferation characteristics of LSPCs, as well as the normal epithelial regeneration. Moreover, we identified that β2-adrenoceptor (Adrb2) was the predominant adrenergic receptor expressed in LSPCs by corneal limbal single-cell sequencing and real time PCR (RT-PCR) analysis of sorted LSPCs. The Adrb2 knockout mice exhibited the enhancement of epithelial regeneration and LSPCs function, compared with the wild-type mice. Similarly, topical application of the Adrb2 specific antagonist ICI 118, 551 effectively accelerated diabetic corneal epithelial regeneration with the restored LSPCs function. Mechanistically, sonic hedgehog (Shh) activity mediated the downstream effects of NE-Adrb2 signaling pathway in regulating LSPCs and epithelial regeneration. Taken together, our data revealed the involvement of sympathetic overactivation in the impairment of diabetic LSPCs function and corneal epithelial regeneration through the NE-Adrb2-Shh signaling pathway. The interference of sympathetic overactivation may provide novel treatment strategies for diabetic keratopathy.

Silk films with nanotopography and extracellular proteins enhance corneal epithelial wound healing

Corneal wound healing depends on extracellular matrix (ECM) and topographical cues that modulate migration and proliferation of regenerating cells. In our study, silk films with either flat or nanotopography patterned parallel ridge widths of 2000, 1000, 800 nm surfaces were combined with ECMs which include collagen type I (collagen I), fibronectin, laminin, and Poly-D-Lysine to accelerate corneal wound healing. Silk films with 800 nm ridge width provided better cell spreading and wound recovery than other size topographies. Coating 800 nm patterned silk films with collagen I proves to optimally further increased mouse and rabbit corneal epithelial cells growth and wound recovery. This enhanced cellular response correlated with redistribution and increase in size and total amount of focal adhesion. Transcriptomics and signaling pathway analysis suggested that silk topography regulates cell behaviors via actin nucleation ARP-WASP complex pathway, which regulate filopodia formation. This mechanism was further explored and inhibition of Cdc42, a key protein in this pathway, delayed wound healing and decreased the length, density, and alignment of filopodia. Inhibition of Cdc42 in vivo resulted in delayed re-epithelization of injured corneas. We conclude that silk film nanotopography in combination with collagen I constitutes a better substrate for corneal wound repair than either nanotopography or ECM alone.

Human platelet lysate delivered via an ocular wound chamber for the treatment of corneal epithelial injuries

Current strategies to address corneal surface defects are insufficient to successfully resolve damage caused by injury and/or disease. To address this issue, we have developed an ocular wound chamber (OWC) that creates a fluid-filled environment by encompassing damaged ocular and periocular tissues allowing for the continuous delivery of therapeutics. This study tested human platelet lysate (hPL) as a treatment for corneal epithelial defects when used with the OWC. Corneal epithelial injuries were created in anesthetized guinea pigs by debridement of the central cornea. An OWC was placed over the injured eye and animals randomly grouped followed by injection of either 20% hPL, 100% hPL, or vehicle (balanced salt solution, BSS) into the chamber. Eyes were assessed at 0, 24, 48, and 72 h using intraocular pressure (IOP), optical coherence tomography (OCT), and fluorescein imaging. Whole globes were histologically processed, and hematoxylin and eosin (H&E) stained. No differences in IOP were recorded as a result of corneal wounding, chamber placement, and/or therapeutic application. OCT images demonstrated increased corneal swelling at 48 h and 72 h in the vehicle group compared to 20% hPL. Fluorescein staining showed increased corneal re-epithelialization in the 20% and 100% hPL groups at 48 h compared to vehicle only. H&E staining revealed increased stromal cellular infiltrate in the BSS group. This study demonstrates the delivery of hPL via the OWC improves corneal re-epithelialization and supports the expanded usage of the chamber in combination with hPL to manage a variety of corneal surface injuries, diseases and/or periocular conditions.

Hyperglycemia-reduced NAD+ biosynthesis impairs corneal epithelial wound healing in diabetic mice

OBJECTIVE

Nicotinamide adenine dinucleotide (NAD) is an essential molecule participating in multiple physiological and pathophysiological processes. In diabetic cornea, the NAD⁺-consuming enzyme SIRT1 was down-regulated and contributed to the delayed wound healing. However, the impact of hyperglycemia on corneal NAD⁺ biosynthesis remained elusive. This study was to investigate the relationship of NAD⁺ biosynthesis and the delayed corneal wound healing in diabetic mice.

METHODS

Type 1 diabetes mellitus (DM) mice were induced by streptozotocin and corneal epithelial wound healing models were constructed by epithelial scraping. The NAD⁺ contents of corneal epithelium were measured using the NAD/NADH quantification kit. Expression of key enzymes involved in the NAD⁺ biosynthesis in type 1 DM mice and type 2 DM patients were analyzed. The nicotinamide phosphoribosyltransferase (NAMPT)-specific siRNA and the selective inhibitor FK866 were used to achieve the blockade of NAMPT, whereas exogenous NAD⁺ and its precursors were replenished to the corneal epithelial cells and DM mice.

RESULTS

Hyperglycemia attenuated NAD⁺ content and NAMPT expression in the corneal epithelium of both type 1 DM mice and type 2 DM patients. Local knockdown of NAMPT by siRNA or FK866 consistently recapitulated the delayed corneal epithelial wound healing in normal mice. Moreover, NAD⁺ replenishment recovered the impaired proliferation and migration capacity by either FK866 or high glucose treatment in cultured corneal epithelial cells. Furthermore, in DM mice, NAD⁺ and its precursors nicotinamide mononucleotide and nicotinamide riboside also facilitated corneal epithelial and nerve regeneration, accompanied with the recovered expression of SIRT1 and phosphorylated EGFR, AKT, and ERK1/2 in epithelium and corneal sensitivity.

CONCLUSION

Hyperglycemia-reduced NAD⁺ biosynthesis and contributed to the impaired epithelial wound healing in DM mice. The replenishment of NAD⁺ and its precursors facilitated diabetic corneal wound healing and nerve regeneration, which may provide a novel therapeutic strategy for the treatment of diabetic corneal complications.

Characterization of limbal explant sites: Optimization of stem cell outgrowth in in vitro culture

Simple limbal epithelial transplantation (SLET) and cultivated limbal epithelial transplantation (CLET) are proven techniques for treating limbal stem cell deficiency (LSCD). However, the precise regions that are most suitable for preparing explants for transplantation have not been identified conclusively. Accordingly, this in vitro study aimed at determining ideal sites to be selected for tissue harvest for limbal stem cell culture and transplantation. We evaluated cell outgrowth potential and the expression of stem cell markers in cultures from 48 limbal explants from five cadaveric donors. The limbal explants were generated from the three specific sites: Lcor (located innermost and adjacent to the cornea), Lm (middle limbus), and Lconj (located outermost adjacent to the conjunctiva). We found that explants from the Lconj and Lm sites exhibited higher growth potential than those from the Lcor site. Transcript encoding the stem cell marker and p63 isoform, ΔNp63, was detected in cells from Lm and Lconj explants; expression levels were slightly, though significantly (p-value < 0.05), higher in Lm than in Lconj, although expression of ΔNp63α protein was similar in cells from all explants. Differential expression of ATP-Binding Cassette Subfamily G Member 2 (ABCG2) did not reach statistical significance. Immunohistochemistry by indirect immunofluorescence analysis of limbus tissue revealed that the basal layer in explant tissue from Lconj and Lm contained markedly more stem cells than found in Lcor explant tissue; these findings correlate with a higher capacity for growth. Collectively, our findings suggest that explants from the Lconj and Lm sites should be selected for limbal cell expansion for both CLET and SLET procedures. These new insights may guide surgeons toward specific limbal sites that are most suitable for stem cell culture and transplantation and may ultimately improve treatment outcomes in the patients with LSCD.

Staphylococcus aureus alpha-hemolysin impairs corneal epithelial wound healing and promotes intracellular bacterial invasion

Colonization by Staphylococcus aureus (S. aureus) has been implicated in many infectious and wound healing disorders. This study was performed to characterize the pathogenic role of S. aureus alpha-hemolysin (alpha-toxin) in corneal epithelial wound healing and infectious keratitis in the setting of a corneal wound. The effect of wild-type and isogenic Hla mutant (α-hemolysin gene deleted) S. aureus bacteria and conditioned media on corneal epithelial wound healing was tested in vitro using a scratch assay and in vivo using a murine epithelial debridement model. The invasiveness of wild-type and Hla mutant S. aureus was evaluated in vitro in human corneal epithelial cells and in vivo in a murine model of infectious keratitis following total epithelial debridement. S. aureus and its conditioned media significantly delayed epithelial wound closure both in vitro (P < 0.05) and in vivo (P < 0.05). The effect of S. aureus on wound healing was significantly diminished with the Hla mutant strain (P < 0.05). Likewise, compared to the wild-type strain, the Hla mutant strain demonstrated significantly reduced ability to invade corneal epithelial cells in vitro (P < 0.05) and infect murine corneas following total epithelial debridement in vivo (P < 0.05). In conclusion, S. aureus alpha-hemolysin plays a major role in the pathologic modulation of corneal epithelial wound healing and the intracellular invasion of the bacteria. Limiting colonization by S. aureus and/or blocking alpha-hemolysin may provide a therapeutic approach for corneal wound healing and infectious disorders.

Aucuba japonica Extract and Aucubin Prevent Desiccating Stress-Induced Corneal Epithelial Cell Injury and Improve Tear Secretion in a Mouse Model of Dry Eye Disease

Dry eye disease is affected by a broad range of causes such as age, lifestyle, environment, medication and autoimmune diseases. These causes induce tear instability that activates immune cells and promotes expression of inflammatory molecules. In this study, we investigated the therapeutic effects of an ethanolic extract of Aucuba japonica (AJE) and its bioactive compound, aucubin, on dry eye disease. The human corneal cells were exposed to desiccation stress induced by exposing cells to air, so that viability was decreased. On the other hand, pre-treatment of AJE and aucubin restored cell survival rate depending on the dose under the dry condition. This result was confirmed again by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining. The mRNA expression of inflammatory molecules was reduced by the pretreatment of AJE and aucubin under the dry state. The therapeutic effects of AJE and aucubin were examined in the animal model for dry eye induced by unilateral excision of the exorbital lacrimal gland. Declined tear volumes and corneal irregularity in the dry eye group were fully recovered by the administration of AJE and aucubin. The apoptotic cells on the cornea were also decreased by AJE and aucubin. Therefore, this study suggests that administration of AJE can be a novel therapeutic for dry eye disease and that the pharmacological activities of AJE may be in part due to its bioactive compound, aucubin.

Corneal Epithelial Deficiency Induced by the Use of β-Blocker Eye Drops

Two studies were conducted to check the effects of β-blocker eye drops, 2% carteolol (Mikelan®) and 0.5% timolol (Timoptol®), on regeneration of corneal epithelium in rabbit eyes. For the short-term study, epithelial deficiency was artificially induced in the cornea of albino rabbits. One of the β-blocker eye drops or 0.005% benzalkonium chloride was applied in the right eye and physiological saline solution was applied to the left eye four times a day, and wound healing rate was calculated. Two weeks later, images of the surface epithelium were analyzed by scanning electron microscopy and proliferative capacity was studied, using proliferating cell nuclear antigen as a marker. The long-term study was conducted similarly except that the eye drops were applied twice a day and epithelial deficiency was re-induced every two weeks.

In the short-term study, epithelial wound healing rate was slowed in β-blocker groups. Significant differences were detected between the Mikelan® and Timoptol® groups, and the benzalkonium and physiological saline groups. The β-blocker groups had severe epithelial cell desquamation, as well as detachment. In the long-term study, the Mikelan® group had significantly delayed wound healing at first induction, the benzalkonium group showed delay up to the third induction and the Timoptol® group up to the fifth induction. These studies indicate that β-blocker eye drops delay corneal epithelial wound healing and supported the concept that corneal epithelial deficiency occurs clinically after the long-term administration of β-blocker eye drops.

Effects of Transforming Growth Factor-Beta 2, Interleukin 6 and Fibronectin on Corneal Epithelial Wound Healing

Purpose

The aim of this study was to compare the effects of topically applied transforming growth factor-beta 2 (TGF-beta 2) and interleukin 6 (IL-6), alone and combined with fibronectin, on the rate of corneal wound healing in rabbits.

Methods

Twenty-eight rabbits were used for the experiment. After the right eye of each rabbit was debrided with n-heptyl alcohol, the animals were divided into four treatment groups (six rabbits per group) and one control group (four rabbits). The debrided eyes were treated, beginning immediately after wounding and continuing every 2 hours from 8 a.m. to 8 p.m. for 48 hours. Group 1 received TGF-beta 2; group 2 IL-6; group 3, TFR-beta 2 and purified fibronectin; group 4, IL-6 and fibronectin; control group, balanced salt solution. At set intervals each eye was stained with fluorescein and photographed; epithelial defects were measured with a computer-assisted digitizer. The healing rate was calculated by linear regression analysis.

Results

The mean healing rates in groups 1, 2, 3, 4, and controls were respectively 1.65 ± 0.16, 1.68 ± 0.11, 1.99 ± 0.12, 2.23 ± 0.09, and 0.93 ± 0.18 mm2/h. Mean epithelial healing rates for all drug-treatment groups were significantly faster than controls. The healing rates of groups 3 and 4 were significantly faster than groups 1 and 2.

Conclusions

We conclude that cytokines, in combination with extracellular matrix proteins, facilitate corneal epithelial wound healing in vivo, possibly by making corneal epithelial cells more sensitive to fibronectin receptors.

Semaphorin3A induces nerve regeneration in the adult cornea-a switch from its repulsive role in development

The peripheral sensory nerves that innervate the cornea can be easily damaged by trauma, surgery, infection or diabetes. Several growth factors and axon guidance molecules, such as Semaphorin3A (Sema3A) are upregulated upon cornea injury. Nerves can regenerate after injury but do not recover their original density and patterning. Sema3A is a well known axon guidance and growth cone repellent protein during development, however its role in adult cornea nerve regeneration remains undetermined. Here we investigated the neuro-regenerative potential of Sema3A on adult peripheral nervous system neurons such as those that innervate the cornea. First, we examined the gene expression profile of the Semaphorin class 3 family members and found that all are expressed in the cornea. However, upon cornea injury there is a fast increase in Sema3A expression. We then corroborated that Sema3A totally abolished the growth promoting effect of nerve growth factor (NGF) on embryonic neurons and observed signs of growth cone collapse and axonal retraction after 30 min of Sema3A addition. However, in adult isolated trigeminal ganglia or dorsal root ganglia neurons, Sema3A did not inhibited the NGF-induced neuronal growth. Furthermore, adult neurons treated with Sema3A alone produced similar neuronal growth to cells treated with NGF and the length of the neurites and branching was comparable between both treatments. These effects were replicated in vivo, where thy1-YFP neurofluorescent mice subjected to cornea epithelium debridement and receiving intrastromal pellet implantation containing Sema3A showed increased corneal nerve regeneration than those receiving pellets with vehicle. In adult PNS neurons, Sema3A is a potent inducer of neuronal growth in vitro and cornea nerve regeneration in vivo. Our data indicates a functional switch for the role of Sema3A in PNS neurons where the well-described repulsive role during development changes to a growth promoting effect during adulthood. The high expression of Sema3A in the normal and injured adult corneas could be related to its role as a growth factor.

The Potential of Gelam Honey in Promoting the Proliferative Phase of Corneal Reepithelialization

INTRODUCTION

Advances in molecular diagnostic medicine have allowed for more rapid, accurate, and comprehensive methods for identifying microorganisms in a chronic wound, which led to the de- velopment and use of a tailored topical antibiotic gel aimed at treating this bioburden.

OBJECTIVE

This is a retrospective chart review evalu- ating the authors' early experience with the use of bacteria-speci c antimicrobial gel therapy on chronic lower extremity wounds that have not responded to standard therapy.

MATERIALS AND METHODS

All patients in the study were treated with a topical gel along with standard of care modalities.

RESULTS

A total of 48 patients with 76 wounds (50/76 venous leg ulcers; 65.8%) were identi ed and analyzed. Of the 48 patients, 11 (22.9%) had complete wound closure at a mean of 101.6 days of treatment. The number of wounds decreasing in size improved from 45.3% to 77.6% after gel therapy. An analysis of all wounds showed an increase in size by 0.7% weekly with the topical gel; how- ever, a mean weekly healing rate of 6.5% was seen when analyzing only the subset of wounds that decreased in size.

CONCLUSIONS

Although a minor improvement of weekly healing rate was seen for a subset of the wounds, the overall wound closure rate was low.

Randomized Controlled Trial of Topical Insulin for Healing Corneal Epithelial Defects Induced During Vitreoretinal Surgery in Diabetics

PURPOSE

To determine the effect of topical insulin of 3 concentrations [0.5, 1, and 2 units per drop 4 times per day (QID)] on postoperative corneal epithelial wound healing in diabetic patients.

DESIGN

A double blind randomized controlled hospital-based study involving diabetic patients with postoperative corneal epithelial defect after vitreoretinal surgery.

METHODS

Diabetic patients were randomized to 3 different concentrations of topical insulin (DTI 0.5, DTI 1, and DTI 2) or placebo in the control group (DNS). Primary outcome measure was the rate of corneal epithelial wound healing (mm² per hour) over pre-set interval and time from baseline to minimum size of epithelial defect on fluorescein stained anterior segment digital camera photography. Secondary outcome measure was any adverse effect of topical insulin. Follow-up was 1 month.

RESULTS

Thirty-two eyes of 32 patients undergoing intraoperative corneal debridement with resultant epithelial defect (8 eyes per group) were analyzed. DTI 0.5 was superior to other concentrations achieving 100% healing rate within 72 hours of treatment compared with 62.5% in DNS, 75% in DTI 1, and 62.5% in DTI 2. Statistically, DTI 0.5 achieved significant results (P = 0.036) compared with the diabetic control group (DNS) in terms of mean rate of corneal epithelial wound healing from maximum to minimum defect size. No adverse effect of topical insulin was reported.

CONCLUSIONS

Topical insulin 0.5 units QID is most effective for healing corneal epithelial defect in diabetic patients after vitrectomy surgery compared with placebo and higher concentrations. Topical insulin is safe for human ocular usage.

Comparison of corneal epitheliotrophic capacities among human platelet lysates and other blood derivatives

PURPOSE

To evaluate the corneal epitheliotropic abilities of two commercialized human platelet lysates (HPLs) and to compare the results with other blood derivatives, including human peripheral serum (HPS) and bovine fetal serum (FBS).

METHODS

In vitro, human corneal epithelial cells were incubated in various concentrations (0%, 3%, 5% and 10%) of blood derivatives. Two commercialized HPLs, including UltraGRO TM (Helios, Atlanta, GA) and PLTMax (Mill Creek, Rochester, MI), were tested and compared with HPS and FBS. Scratch-induced directional wounding assay was performed to evaluate cellular migration. MTS assay was used to evaluate cellular proliferation. Cellular differentiation was examined by scanning electron microscopy, inverted microscopy and transepithelial electrical resistance. Sprague-Dawley rats were used to evaluate the effects of the blood derivatives on corneal epithelial wound healing in vivo. Different blood derivatives were applied topically every 2 hours for 2 days after corneal epithelial debridement. The concentrations of epidermal growth factor (EGF), transforming growth factor -β1 (TGF-β1), fibronectin, platelet-derived growth factor-AB (PDGF-AB), PDGF-BB, and hyaluronic acid in different blood derivatives were evaluated by enzyme-linked immunosorbent assay (ELISA).

RESULTS

In vitro experiments demonstrated statistically comparable epitheliotropic characteristics in cellular proliferation, migration, and differentiation for the two commercialized HPLs compared to FBS and HPS. Cells cultured without any serum were used as control group. The epitheliotropic capacities were statistically higher in the two commercialized HPLs compared to the control group (p<0.05). Among the different concentrations of blood derivatives, the preparations with 3% yielded better outcomes compared to 5% and 10%. In rats, HPLs also caused improved but not statistically significant wound healing compared to HPS. All the blood derivatives had better wound healing ratios than the control group (p<0.05). In the quantification of epitheliotropic factors, UltraGRO and PLTMax had significantly higher levels of EGF, TGF- β1, fibronectin than human peripheral serum (p<0.05).

CONCLUSIONS

Both commercialized HPLs showed comparable corneal epitheliotropic abilities and wound healing rates compared to HPS and FBS in the in vivo and in vitro studies. Our results suggest that HPLs may have the potential to replace HPS in the treatment of corneal epithelial problems.

Effects of Granulocyte-Macrophage Colony-Stimulating (GM-CSF) Factor on Corneal Epithelial Cells in Corneal Wound Healing Model

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a pleiotropic cytokine that activates granulocyte and macrophage cell lineages. It is also known to have an important function in wound healing. This study investigated the effect of GM-CSF in wound healing of human corneal epithelial cells (HCECs). We used human GM-CSF derived from rice cells (rice cell-derived recombinant human GM-CSF; rhGM-CSF). An in vitro migration assay was performed to investigate the migration rate of HCECs treated with various concentrations of rhGM-CSF (0.1, 1.0, and 10.0 μg/ml). MTT assay and flow cytometric analysis were used to evaluate the proliferative effect of rhGM-CSF. The protein level of p38MAPK was analyzed by western blotting. For in vivo analysis, 100 golden Syrian hamsters were divided into four groups, and their corneas were de-epithelialized with alcohol and a blade. The experimental groups were treated with 10, 20, or 50 μg/ml rhGM-CSF four times daily, and the control group was treated with phosphate-buffered saline. The corneal wound-healing rate was evaluated by fluorescein staining at the initial wounding and 12, 24, 36, and 48 hours after epithelial debridement. rhGM-CSF accelerated corneal epithelial wound healing both in vitro and in vivo. MTT assay and flow cytometric analysis revealed that rhGM-CSF treatment had no effects on HCEC proliferation. Western blot analysis demonstrated that the expression level of phosphorylated p38MAPK increased with rhGM-CSF treatment. These findings indicate that rhGM-CSF enhances corneal wound healing by accelerating cell migration.

A Comparative Study of the Therapeutic Potential of Mesenchymal Stem Cells and Limbal Epithelial Stem Cells for Ocular Surface Reconstruction

Stem cell-based therapy has become an attractive and promising approach for the treatment of severe injuries or thus-far incurable diseases. However, the use of stem cells is often limited by a shortage of available tissue-specific stem cells; therefore, other sources of stem cells are being investigated and tested. In this respect, mesenchymal stromal/stem cells (MSCs) have proven to be a promising stem cell type. In the present study, we prepared MSCs from bone marrow (BM-MSCs) or adipose tissue (Ad-MSCs) as well as limbal epithelial stem cells (LSCs), and their growth, differentiation, and secretory properties were compared. The cells were grown on nanofiber scaffolds and transferred onto the alkali-injured eye in a rabbit model, and their therapeutic potential was characterized. We found that BM-MSCs and tissue-specific LSCs had similar therapeutic effects. Clinical characterization of the healing process, as well as the evaluation of corneal thickness, re-epithelialization, neovascularization, and the suppression of a local inflammatory reaction, were comparable in the BM-MSC- and LSC-treated eyes, but results were significantly better than in injured, untreated eyes or in eyes treated with a nanofiber scaffold alone or with a nanofiber scaffold seeded with Ad-MSCs. Taken together, the results show that BM-MSCs' therapeutic effect on healing of injured corneal surface is comparable to that of tissue-specific LSCs. We suggest that BM-MSCs can be used for ocular surface regeneration in cases when autologous LSCs are absent or difficult to obtain.

SIGNIFICANCE

Damage of ocular surface represents one of the most common causes of impaired vision or even blindness. Cell therapy, based on transplantation of stem cells, is an optimal treatment. However, if limbal stem cells (LSCs) are not available, other sources of stem cells are tested. Mesenchymal stem cells (MSCs) are a convenient type of cell for stem cell therapy. The therapeutic potential of LSCs and MSCs was compared in an experimental model of corneal injury, and healing was observed following chemical injury. MSCs and tissue-specific LSCs had similar therapeutic effects. The results suggest that bone marrow-derived MSCs can be used for ocular surface regeneration in cases when autologous LSCs are absent or difficult to obtain.

The effects of recombinant human epithelialgrowth factor and protein-free calf blood extract for recovery of corneal mechanical epithelial defects healing and neovascularization

OBJECTIVE

This study was undertaken to investigate the effects of recombinant human epidermal growth factor (rhEGF) and protein-free calf blood extract on corneal wound healing and neovascularization.

MATERIALS AND METHODS

An rabbit central corneal wound and neovascularization model was established in rabbits. One eye of each group was chosen randomly for topical administration of protein-free calf blood extract, rhEGF, or NS (physiological saline), and variability in the area of corneal epithelial wound healing and neovascularization was observed.

RESULTS

On days 1 and 2, the healing rate of corneal epithelium was various among the protein-free calf blood extract group, rhEGF group and NS group (F=6.475, p=0.012). The healing rate of corneal epithelium in the rhEGF group was better than the protein-free calf blood extract group (p=0.004) and NS group (p=0.041) on day 1. The corneal neovascularization area in the protein-free calf blood extract group was less than that of rhEGF group (p=0.04) and NS group (p=0.008) on day 18.

CONCLUSIONS

rhEGF had better promotive effect on corneal epithelial wound healing than the protein-free calf blood extract in the advanced phase (within 2 days). Both rhEGF and protein-free calf blood extract were not found to promote.

New trends in quantitative assessment of the corneal barrier function

The cornea is a very particular tissue due to its transparency and its barrier function as it has to resist against the daily insults of the external environment. In addition, maintenance of this barrier function is of crucial importance to ensure a correct corneal homeostasis. Here, the corneal epithelial permeability has been assessed in vivo by means of non-invasive tetrapolar impedance measurements, taking advantage of the huge impact of the ion fluxes in the passive electrical properties of living tissues. This has been possible by using a flexible sensor based in SU-8 photoresist. In this work, a further analysis focused on the validation of the presented sensor is performed by monitoring the healing process of corneas that were previously wounded. The obtained impedance measurements have been compared with the damaged area observed in corneal fluorescein staining images. The successful results confirm the feasibility of this novel method, as it represents a more sensitive in vivo and non-invasive test to assess low alterations of the epithelial permeability. Then, it could be used as an excellent complement to the fluorescein staining image evaluation.

Involvement of pigment epithelium-derived factor, docosahexaenoic acid and neuroprotectin D1 in corneal inflammation and nerve integrity after refractive surgery

Alterations in corneal innervations result in impaired corneal sensation, severe dry eye and damage to the epithelium that may in turn lead to corneal ulcers, melting and perforation. These alterations can occur after refractive surgery. We have discovered that pigment epithelium-derived factor (PEDF) plus docosahexaenoic acid (DHA or the docosanoid bioactive neuroprotectin D1 (NPD1)) induces nerve regeneration after corneal surgery that damages the stromal nerves. We found that PEDF is released from corneal epithelial cells after injury, and when DHA is provided to the cells it stimulates the biosynthesis of NPD1 by an autocrine mechanism. The combination of PEDF plus DHA also decreased the production of leukotriene B4 (LTB4), a neutrophil chemotactic factor, thereby decreasing the inflammation induced after corneal damage. These studies suggest that PEDF plus DHA and its derivative NPD1 hold promise as a future treatment to restore a healthy cornea after nerve damage.

Lumican promotes corneal epithelial wound healing

Lumican regulates collagenous matrix assembly as a keratan sulfate proteoglycan in the cornea and is also present in the connective tissues of other organs and embryonic corneal stroma as a glycoprotein. In normal unwounded cornea, lumican is expressed by stromal keratocytes. Interestingly, injured mouse corneal epithelium ectopically and transiently expresses lumican during the early phase of wound healing, suggesting a potential lumican functionality unrelated to regulation of collagen fibrillogenesis, e.g., modulation of epithelial cell adhesion or migration. Healing of a corneal epithelial injury in lumican knockout (Lum(-/-)) mice was significantly delayed compared with Lum(+/-) mice. Addition of purified lumican to cultured medium promoted re-epithelialization and enhanced cell proliferation of wild-type mouse corneal epithelial cells in an organ culture. Therefore, administration of lumican may be beneficial for treating epithelial defects in the cornea and other tissues.

CCL20, γδ T cells, and IL-22 in corneal epithelial healing

After corneal epithelial abrasion, leukocytes and platelets rapidly enter the corneal stroma, and CCR6(+) IL-17(+) γδ T cells migrate into the epithelium. γδ T-cell-deficient (TCRδ(-/-)) mice have significantly reduced inflammation and epithelial wound healing. Epithelial CCL20 mRNA increased 19-fold at 3 h, and protein increased ∼ 16-fold at 6 h after injury. Systemic or topical treatment of wild-type C57BL/6 mice with anti-CCL20 reduced γδ T-cell accumulation in the cornea by >50% with a concomitant decrease in epithelial healing and stromal inflammation. In addition to CCR6 and IL-17, corneal γδ T cells stained positively for RORγt, IL-23R, and IL-22. Anti-IL-22 reduced peak cell division of the healing epithelium by 52%. Treatment of TCRδ(-/-) mice with rIL-22 significantly promoted wound closure, with peak epithelial cell division increased >3-fold. In addition, rIL-22 restored neutrophil and platelet influx in the TCRδ(-/-) mice to wild-type levels and increased CXCL1 production by wounded corneal explants >2-fold. These results indicate that an important aspect of the healing response to corneal epithelial abrasion includes CCL20-dependent influx of CCR6(+) IL-17(+) IL-22(+) γδ T cells and that IL-22 contributes to the inflammatory response and promotes epithelial healing.

Effects of ultra high molecular weight poly-gamma-glutamic acid from Bacillus subtilis (chungkookjang) on corneal wound healing

Poly-gamma-glutamic acid (gamma-PGA) is a natural, edible polypeptide in which glutamate is polymerized via gamma-amide linkages. First, we assessed the eye irritancy potential of gamma PGA in rabbits. Additionally, we studied the effects of gamma-PGA on corneal wound healing, due to the anti inflammatory properties and water retaining abilities of gamma-PGA. In this study, the effects of gamma-PGA on corneal wound healing after an alkali burn were evaluated. Thirty eyes wounded by alkali burning in 30 white rabbits were divided into three groups: group A was treated with 0.1% 5000 kDa gamma-PGA for 2 days, group B was treated with 0.1% hyaluronic acid, and group C was not treated, as a control. The area of corneal epithelial defect was examined at 12, 24, 30, 36, 42, and 48 h after corneal alkali wounding to determine initial wound healing. We found that gamma-PGA promoted corneal wound healing, compared with controls, and showed similar effects to hyaluronic acid. These results indicate that gamma-PGA stimulates corneal wound healing by an anti inflammatory effect and enhancing cell migration and cell proliferation. gamma-PGA is a promising biomaterial that may be a substitute for hyaluronic acid in corneal wound healing treatment.

Early keratocyte apoptosis after epithelial scrape injury in the human cornea

Animal studies in mice, rats, rabbits, pigs and hens demonstrated that anterior keratocytes undergo programmed cell death or apoptosis after corneal epithelial injury. Many other wound healing changes subsequently follow the keratocyte apoptosis response. This study evaluated early keratocyte apoptosis after corneal epithelial scrape injury in human eyes scheduled for enucleation for malignancy. Two eyes had corneal epithelial scrape 1 h prior to the enucleation and another eye served as a control and had no corneal scrape prior to enucleation. One additional eye was enucleated, washed with balanced salt solution, and then had the corneal epithelium scraped 1 h prior to processing for analysis. Apoptosis was identified by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay and confirmed by transmission electron microscopy (TEM). Anterior keratocyte apoptosis was detected in the three corneas that had epithelial scrape injury, but not in the control unwounded cornea. This study confirmed that keratocyte apoptosis is also an early response to corneal epithelial injury in humans and showed that tears are not essential for keratocyte apoptosis to occur in response to epithelial injury.

High glucose suppresses epidermal growth factor receptor/phosphatidylinositol 3-kinase/Akt signaling pathway and attenuates corneal epithelial wound healing

OBJECTIVE

Patients with diabetes are at an increased risk for developing corneal complications and delayed wound healing. This study investigated the effects of high glucose on epidermal growth factor receptor (EGFR) signaling and on epithelial wound healing in the cornea.

RESEARCH DESIGN AND METHODS

Effects of high glucose on wound healing and on EGFR signaling were investigated in cultured porcine corneas, human corneal epithelial cells, and human corneas using Western blotting and immunofluorescence. Effects of high glucose on reactive oxygen species (ROS) and glutathione levels and on EGFR pathways were assessed in porcine and primary human corneal epithelial cells, respectively. The effects of EGFR ligands and antioxidants on high glucose-delayed epithelial wound healing were assessed in cultured porcine corneas.

RESULTS

High glucose impaired ex vivo epithelial wound healing and disturbed cell responses and EGFR signaling to wounding. High glucose suppressed Akt phosphorylation in an ROS-sensitive manner and decreased intracellular glutathione in cultured porcine corneas. Exposure to high glucose for 24 h resulted in an increase in ROS-positive cells in primary human corneal epithelial cells. Whereas heparin-binding EGF-like growth factor and antioxidant N-acetylcysteine had beneficial effects on epithelial wound closure, their combination significantly accelerated high glucose-delayed wound healing to a level similar to that seen in control subjects. Finally, Akt signaling pathway was perturbed in the epithelia of human diabetic corneas, but not in the corneas of nondiabetic, age-matched donors.

CONCLUSIONS

High glucose, likely through ROS, impairs the EGFR-phosphatidylinositol 3-kinase/Akt pathway, resulting in delayed corneal epithelial wound healing. Antioxidants in combination with EGFR ligands may be promising potential therapeutics for diabetic keratopathy.

BALB/c and C57BL6 mouse strains vary in their ability to heal corneal epithelial debridement wounds

Genetically engineered mice are usually produced on a mixed genetic background and can be derived from several mouse strains including 129SvJ, C57BL6, and BALB/c. To determine whether differences in recurrent corneal epithelial erosions (RCEEs), corneal epithelial stem cell deficiency (CESCD), and cell migration rate vary between two different mouse strains (BALB/c and C57BL6), 8-week mice were subjected to 1.5 (small) or 2.8mm (large) manual debridement wounds and allowed to heal for 4 weeks. Syndecan-1 (sdc-1) null mice backcrossed seven generations onto a BALB/c genetic background were also included in the RCEE and CESCD studies to permit comparisons between genotypes within a single strain. After sacrifice, corneas were assessed for the presence of recurrent erosions; no fewer than 15 corneas were used for each strain or genotype studied. Data show that the frequency of recurrent erosions after small wounds was 81+/-9% in the C57BL6 mice, 73+/-2% in the BALB/c mice, and 32+/-6% in sdc-1 null mice. Neither strain developed CESCD after small wounds. The frequency of erosions after large wounds was greater (88+/-8%) in the C57BL6 mice compared to BALB/c (60+/-2%), and sdc-1 null mice (32+/-5%). Four weeks after the large wounds, fixed, flat mounted corneas were assessed for evidence of CESCD with antibodies against the conjunctival keratin K8 and the goblet cell marker, the mucin Muc5AC. The frequency of CESCD 4 weeks after the large wounds was significantly greater in the C57BL6 mice than in the BALB/c or sdc-1 null mice. To assess cell migration rates, corneas were subjected to 1.5mm wounds and allowed to heal for 12, 15, 18, 21, and 24h. After sacrifice, corneas were stained with Richardson stain (BALB/c) or propidium iodide (C57BL6) to assess reepithelialization rates. While reepithelialization rates were similar for the early times after wounding, by 24h the C57BL6 corneas had healed faster: 16 of 30 corneas from the C57BL6 mice were closed compared to 9 of 30 of the BALB/c wounds. BALB/c corneas appeared larger overall compared to C57BL6 corneas; measurements of the overall mass of the enucleated eyes and diameters of the flat-mounted corneas confirmed that C57BL6 eyes and corneas were 6.8% and 4.4% smaller respectively than those of BALB/c mice even though the masses of the two mouse strains at 8 weeks of age were identical. Using BrdU to label dividing cells, we found that 18 h after wounding, C57BL6 and BALB/c corneal epithelia showed similar numbers of proliferating cells. To determine if the enhanced corneal epithelial cell migration rate seen in the C57BL6 mice was specific to the cornea, we conducted time-lapse studies to assess random cell migration rates in vitro using primary cultures of mouse epidermal keratinocytes. Consistent with the in vivo data, epidermal keratinocytes derived from BALB/c mice migrated 60% slower than C57BL6 cells. These data prove that strain-specific differences in cell migration rate in vivo are present in the cornea and are accompanied by differences in the frequencies of recurrent erosions and corneal epithelial stem cell deficiency.

[Efficacy of protein-free calf blood extract for mechanical corneal epithelial defects in human eyes]

OBJECTIVE

To evaluate the clinical efficacy between protein-free calf blood extract eye drops and recombinant human epidermal growth factor (rhEGF) eye drops for mechanical corneal epithelial defects in human eyes.

METHODS

A multi-center, randomized and double-blind study with a parallel, positive-control designation was carried out from April to November in 2005 at Department of Ophthalmology, Eye Ear Nose and Throat Hospital of Fudan University, Xinhua Hospital of Shanghai Jiaotong University, the First Hospital of Zhejiang University, the Second Hospital of Zhejiang University and Qingdao Municipal Hospital. 240 patients (240 eyes) with confirmed diagnosis of corneal epithelial defects at that six hospitals were enrolled in this study and were randomly arranged into two groups in average. One group (120 eyes) were treated by 20% protein-free calf blood extract eye drops which was defined as the experimental group while the other (120 eyes) by 5000 IU/ml recombinant human epidermal growth factor (rhEGF) eye drops as the positive control group. The drug was delivered in both groups 4 times per day, one drop each time in the 14 days duration. The symptoms and signs were scored and the safety was evaluated on the pre-delivery day, the third post-delivery day (day 3), day 7 and day 14. The variants in the study were tested for the different efficacy and safety between the two drugs using non-inferiority test, paired t-test, Wilcoxon signed-rank test, chi-square test, continuity correction chi-square test, Fisher's exact probabilities, analysis of variance, Cochran-Mantel-Haenszel chi-square test and so on. The criterion for statistical significance was P < 0.05.

RESULTS

There was no significant difference in efficacy between the protein-free calf blood extract group and the recombinant human epidermal growth factor group (day 3: X2 = 1.5677, P = 0.4566, day 7: X2 = 1.7152, P = 0.4242, day 14: X2 = 3.0814, P = 0.2142). The total scores of symptoms and signs in experimental group had a obvious descending (6.009 +/- 3.030) compared with the positive control group with a descending of (5.177 +/- 2.582), which reached the significant level (t = 2.2367, P = 0.0263). Ocular local stimulates and general side effect were not observed within the treatment course. There was no significant difference between the two groups in the comparison of pre- and post-therapy visual acuity. The difference was not significant when comparing the uncomfortable feelings, including eye burning and eye itching (eye burning: day 3: X2 = 0.4394, P = 0.932, day 7: X2 = 1.4710, P = 0.479,day 14: X2 = 2.1875, P= 0.335, and eye itching: day 3: X2 = 2.1045, P = 0.349, day 7: X2 = 2.0192, P = 0.364, day 14: X2= 0.6863, P = 0.407). And the positive control group gave priority to the experimental group in comfortability. A better comfortableness was reported in the protein-free calf blood extract group on the third day post-delivery (X2 = 6.626, P = 0.0100). However, no obvious difference was examined on day 7 and day 14 post-delivery.

CONCLUSION

Protein-free calf blood extract eye drops has confirmed efficacy, good safety, quick effect and better comfortableness.

[Methods for reducing traumatism of the posterior corneal epithelium during ultrasound phacoemulsification]

[Methods for reducing traumatism of the posterior corneal epithelium during ultrasound phacoemulsification]

Goldmann applanation tonometry over daily disposable contact lens: Accuracy and safety of procedure

PURPOSE

To study accuracy and safety, related to sensation (discomfort) and trauma, when using Goldmann applanation tonometry (GAT) on eyes wearing daily disposable soft contact lenses.

METHODS

The intra-ocular pressure (IOP) of 136 normal eyes of 68 subjects was measured by Goldmann tonometer. Measurements were made in one eye with a contact lens (hilafilcon A) without anaesthetic drops and then without the contact lens using one drop of 0.4% oxybuprocaine hydrochloride. Each contact lens used was identical as to back optic zone, back vertex power. Standard Goldmann procedure only was used for the fellow eye of each subject. Subjective sensation (discomfort) responses to both procedures were studied in a subgroup (66 eyes) using a scale of discomfort, from 1 (no sensation) to 5 (highest sensation). Epithelial staining after tonometry was evaluated for this subgroup.

RESULTS

No significant differences were found for the IOP with and without contact lens (t<1; p=0.63) for the IOP range studied. There was a good correlation between the two procedures (r=0.81; p<0.05). Lowest sensation was found with tonometry on the anaesthetized cornea; this condition was significantly different from other conditions (p<0.005). No difference was found among the other conditions (contact lens insertion, tonometry on contact lens and application of topical anaesthetic). Corneal epithelial staining following the standard tonometry procedure was significantly higher than following the procedure with a contact lens (p<0.00005).

CONCLUSIONS

Measurement of IOP by GAT over a daily disposable soft contact lens is accurate, compared to the standard procedure and within the IOP's normal range studied here. Also using a contact lens results in less trauma whilst discomfort is similar.

Use of Topical Insulin to Normalize Corneal Epithelial Healing in Diabetes Mellitus

OBJECTIVE

To determine whether topical application of insulin normalizes delayed corneal wound healing in rats with diabetes mellitus (DB).

METHODS

Diabetes mellitus was induced with streptozocin. A 5-mm corneal abrasion at 9 or 11 weeks was treated topically for 7 days (4 times daily) with 1, 2, or 5 U of insulin or with sterile vehicle (SV).

RESULTS

Residual corneal epithelial defects of rats with DB receiving SV (hereafter called DB SV rats or animals) were approximately 35% larger than in healthy animals receiving SV (hereafter called healthy SV rats or animals). Rats with DB receiving topical insulin had wounds ranging from 19% to 60% smaller than DB SV rats, corresponding to wound sizes in healthy SV rats. Topical insulin had no effect on reepithelialization of corneal wounds in healthy SV rats. Insulin did not affect corneal thickness, ocular pressure, or serum glucose level. The corneal sensitivity of DB SV rats was markedly reduced from healthy SV rats, but rats with DB given insulin had corneal sensitivity values comparable to the healthy SV group. DNA synthesis was decreased in DB SV corneal epithelium but was comparable to that in healthy SV rats after they received insulin; apoptosis and necrosis levels were similar in all groups.

CONCLUSION

Topical insulin normalizes corneal reepithelialization in diabetic rats.

CLINICAL RELEVANCE

Direct application of insulin may serve as an important strategy for treating diabetic keratopathy.

Amniotic membrane transplantation for the management of corneal epithelial defects: an in vivo confocal microscopic study

PURPOSE

To evaluate amniotic membrane (AM) tissue morphology and corneal epithelial healing in human eyes after amniotic membrane transplantation (AMT), using laser scanning in vivo confocal microscopy (IVCM).

PATIENTS AND METHODS

Twenty eyes of 20 patients, treated with single layer epithelial side up AMT for chemical burns in the acute stage (n = 8) and persistent corneal epithelial defect (n = 12) were studied by serial IVCM post-AMT until complete re-epithelisation. Changes in morphology of transplanted amniotic tissue and healing corneal epithelium were noted. AM and corneal epithelial cell density was calculated using image-analysis software.

RESULTS

IVCM enabled visualisation of transplanted AM and of regenerating epithelial cells under the AM. The mean AM epithelial cell density, 1 day after transplant, was 4613 (SD 380) cells/mm2. The average AM epithelial thickness was 35 (4) microm, while the AM stromal thickness was 116 (31) microm. The amniotic stroma appeared to be composed of a superficial dense fibrous layer and a deeper loose reticular network of fibres. Amniotic epithelium was lost within 15 days of transplant, and complete re-epithelisation of the corneal surface was achieved between 1 and 4 weeks.

CONCLUSIONS

Laser scanning IVCM is a useful method for evaluating AM tissue morphology, degradation and corneal epithelial healing after AMT for different clinical indications. When the amniotic membrane acts as a patch, that is epithelial cells migrate under rather than over the membrane, the membrane disintegrates and is lost.

Ocular surface changes in limbal stem cell deficiency caused by chemical injury: a histologic study of excised pannus from recipients of cultured corneal epithelium

PURPOSE

To report histopathologic changes of the ocular surface pannus in patients with severe limbal stem cell deficiency (LSCD).

METHODS

Corneal and conjunctival pannus tissues from 29 patients undergoing ocular reconstruction with cultured limbal cell transplantation were included. The medical records of these patients were reviewed for demographics, aetiologic diagnosis, type of injury, interval between the initial insult and excision of pannus, and medical history involving human amniotic membrane (HAM) or limbal transplantation. The paraffin-embedded tissues were reviewed for epithelial changes, type-degree of fibrosis, degenerative changes, vascular changes, conjunctivalization of corneal surface, and evidence of residual HAM. We attempted a clinicopathologic correlation to understand the pathogenesis of pannus formation in LSCD.

RESULTS

The 29 tissues were from 29 eyes of patients with primary aetiology of chemical burn in 89.6% (undetermined in 10.4%) of cases. The pannus showed epithelial hyperplasia in 62%, active fibrosis in 66%, severe inflammation in 21%, giant cell reaction in 28%, and stromal calcification in 14% cases. Goblet cells were seen over the cornea in 64% cases; their absence was associated with squamous metaplasia of the conjunctiva and with long duration of insult. Evidence of residual HAM was noted in 42% cases.

CONCLUSIONS

The commonest cause of severe LSCD is alkali-induced injury. Goblet cells over the cornea were seen in 60% of cases. HAM used for ocular surface reconstruction could persist for long periods within the corneal pannus, thus raising the need for further studies with long-term follow-up.

Stimulation of corneal epithelial migration by a synthetic peptide (PHSRN) corresponding to the second cell-binding site of fibronectin

PURPOSE

Fibronectin plays an important role in the migration of corneal epithelial cells in vivo. The Arg-Gly-Asp (RGD) sequence in the principal cell binding domain of fibronectin mediates the interaction of fibronectin with integrins, whereas the Pro-His-Ser-Arg-Asn (PHSRN) sequence of fibronectin is thought to modulate this interaction. The authors examined the effects of a PHSRN peptide on corneal epithelial migration in vitro and in vivo.

METHODS

Epithelial migration in vitro was examined with the rabbit cornea in organ culture. The motility and phenotype of simian virus 40-transformed human corneal epithelial (HCE) cells were evaluated by time-lapse and immunofluorescence microscopy, respectively. Tyrosine phosphorylation of focal adhesion kinase (FAK) and paxillin was examined by immunoprecipitation and immunoblot analysis. The healing of rabbit corneal epithelial wounds induced by 1-heptanol was evaluated by fluorescein staining.

RESULTS

The PHSRN peptide stimulated corneal epithelial migration in organ culture in a concentration-dependent manner, and it increased HCE cell motility in vitro. The peptide induced the accumulation of F-actin and the formation of focal adhesions at the leading edge of HCE cells. It also upregulated the tyrosine phosphorylation of FAK and paxillin in HCE cells, but it did not affect HCE cell proliferation or attachment to a fibronectin matrix. Administration of the PHSRN peptide in eye drops promoted corneal epithelial wound closure in vivo in a dose-dependent manner. None of these effects of the PHSRN peptide were induced by a control NRSHP peptide.

CONCLUSIONS

The PHSRN peptide mimics many of the effects of fibronectin on corneal epithelial cells and may prove suitable as a substitute for fibronectin in the treatment of persistent corneal epithelial defects.

Carboxymethylcellulose Binds to Human Corneal Epithelial Cells and Is a Modulator of Corneal Epithelial Wound Healing

PURPOSE

In this study, the ability of carboxymethylcellulose (CMC), used in artificial tear formulations, to interact with corneal-epithelial-cells (HCECs) and facilitate corneal epithelial wound healing was investigated.

METHODS

HCECs were incubated with fluorescein-labeled CMC (F-CMC). CMC-epithelial binding was measured by spectrophotometry. The effect on F-CMC binding by hyaluronic acid (HA) or glucose was measured after preincubation in HA, mAb to CD44, or glucose, or mAb to GluT-1. F-CMC binding to fibronectin or collagen was measured by incubating proteins with F-CMC. The wound widths were measured 18 hours after confluent HCECs were scratch wounded. The ability of CMC to induce cell chemotaxis, proliferation, or migration was measured by quantitative assay. The efficacy of CMC in promoting epithelial wound healing was also tested in a rabbit epithelial scrape-wound model.

RESULTS

CMC remained bound to the HCECs for 2 hours. Preincubation of HCECs with glucose or mAb to GluT-1, but not with HA or mAb to CD44, reduced the binding of CMC to HCECs from 43.7% to 67.2% or 10.9% to 25.3%, respectively. CMC bound significantly to fibronectin (3.1-fold) or collagen (9.3-fold) compared with the control (BSA), and such binding enhanced cell adhesion. CMC stimulated re-epithelialization of HCECs scratched in vitro and in vivo rabbit cornea epithelial scrape wounds. CMC stimulated cell migration but not proliferation.

CONCLUSIONS

CMC probably binds to HCECs through interaction of its glucopyranose subunits with glucose transporters. CMC binding to the matrix proteins stimulated HCEC attachment, migration, and re-epithelialization of corneal wounds.

Interdependence of lipoxin A4 and heme-oxygenase in counter-regulating inflammation during corneal wound healing

In the immune-privileged cornea, epithelial wounds heal rapidly with almost no scarring and, unlike in most other tissues, acute inflammation in the absence of infection is beneficial to healing. Molecular mechanisms, which account for this striking property, remain to be clearly defined, but they likely include autacoids that control leukocyte activation. Two prominent enzymes, 12/15-lipoxygenase (LOX), which generates antiinflammatory lipid autacoids, and heme-oxygenase (HO), which generates antioxidants and carbon monoxide, are highly expressed in human and mouse corneas. LXA4, an endogenous 12/15-LOX product, proved to be a potent inhibitor of exacerbated inflammation and significantly increased re-epithelialization in corneal wounds. In vivo deletion of 12/15-LOX correlated with exacerbated inflammation and impaired wound healing in 12/15-LOX(-/-) mice, a phenotype that was rescued by treatment with LXA4. More importantly, 12/15-LOX(-/-) mice demonstrated impaired induction of HO-1 in both acute and exacerbated inflammation. Topical LXA4 restored HO-1 expression in 12/15-LOX(-/-) mice and amplified HO-1 gene expression in human corneal epithelial cells. HO-2(-/-) mice, which fail to induce HO-1, also demonstrated exacerbated inflammation in response to injury, a phenotype that, notably, correlated with a 50% reduction in endogenous LXA4 formation. Collectively, results demonstrate a critical role for LXA4 in inflammatory/reparative responses and provide the first evidence that 12/15-LOX and HO systems function in concert to control inflammation.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

The role of the slug transcription factor in cell migration during corneal re-epithelialization in the dog

Epithelial cell migration during corneal wound re-epithelialization shares features with the developmental process of epithelial-mesenchymal transition (EMT) modulated by Snail family transcription factors, including Slug. Our studies demonstrated that Slug expression was enhanced at sites of epithelial cell migration at the margins of normally healing corneal wounds in dogs, but significantly decreased at the margins of non-healing canine corneal erosions. Increased Slug expression was associated with internalization of E-cadherin and beta-catenin from the cell membrane and with enhanced expression of smooth-muscle-specific alpha-actin, tropomyosin, and matrix metalloproteinases at wound margins. Enhanced Slug expression in corneal explants due to an adenoviral expression construct or to oxytetracycline treatment resulted in significantly higher rates of corneal epithelial cell migration. Oxytetracycline appeared to act by stimulating transforming growth factor-beta activity, thus increasing Slug expression and enhancing corneal epithelial migration. These findings highlight the similarities between epithelial migration during EMT and during successful corneal wound healing, support an important role for the Snail family in the process, and indicate that modulating Slug expression may be clinically useful in treating non-healing corneal wounds.

Changes in albumin precursor and heat shock protein 70 expression and their potential role in response to corneal epithelial wound repair

Many proteins displayed differential expression (either up- or down-regulation) when proteome of migrating and non-migrating epithelium was assessed using 2-DE and ESI-Q-TOF MS/MS. From the up-regulated set, we have identified for the first time a 69-kDa albumin precursor protein with four peptides sequences and 70-kDa heat shock protein (hsp70) with one peptide in the active phase of cell migration (48 h) during the healing process. Western blot analysis was used to further characterize these proteins at different phases (24, 48 and 72 h) of healing. An increase in the mRNA expression (measured using RT-PCR) in the active migration phase (48 h) for albumin precursor and hsp70 was also observed. Furthermore, co-immunoprecipitation studies with anti-albumin precursor and anti-hsp70 antibodies, followed by immunoblotting with anti-fibronectin antibody demonstrated a novel and biologically relevant interaction between albumin precursor protein and fibronectin in corneal epithelial wound healing but not with hsp70. The increased gene and protein expression of albumin and hsp70 during the active phase of cell migration (48 h) in the corneal epithelium suggests their possible role in corneal wound healing. These findings may have broader implications for developing therapeutic strategies for treating wound healing disorders.

Transactivation of EGFR mediates insulin-stimulated ERK1/2 activation and enhanced cell migration in human corneal epithelial cells

PURPOSE

Insulin activates phosphatidylinositol 3-kinase (PI3K) and extracellular signal-regulated kinase (ERK)-1/2 in human corneal epithelial cells. These events have been shown to be involved in wound healing. However, the mechanism of insulin-induced ERK pathway is not clear during corneal wound healing. In this study, the effect of insulin associated with epidermal growth factor receptor (EGFR) on wound healing in transformed human corneal epithelial cells was investigated to determine the signaling mechanism involved.

METHODS

SV40-immortalized human corneal epithelial (THCE) cells were cultured on a diluted Matrigel matrix that resembled the basement membrane of the corneal epithelium. A wound was introduced with a micropipette tip, and closure of the scratch wound was photographed 12 h after exposure to insulin. Activation of EGFR was analyzed by immunoprecipitation, and cytoskeletal rearrangements were visualized with rhodamine-conjugated phalloidin.

RESULTS

Exposure of corneal epithelial cells to insulin induced phosphorylation of EGFR. Inhibition of EGFR activation by AG1478 or the MMP inhibitor, GM6001, reduced phosphorylation of insulin-induced ERK in the presence of insulin and delayed wound closure. In addition, cells exposed to insulin contained stress fibers and their submembranous cortical actin was depleted. These effects were inhibited by AG1478.

CONCLUSIONS

Inhibition of EGFR activity decreases cell migration involved in insulin-induced wound repair, an effect that mimics inhibition of MMP activation. Inhibition of MMP activity leads to decreased EGFR phosphorylation. Our data show that insulin stimulates wound healing in the corneal epithelium by activating EGFR, and point to a novel insulin signaling pathway that acts during corneal wound healing.

Expression of the gene encoding poly(ADP-ribose) polymerase-1 is modulated by fibronectin during corneal wound healing

PURPOSE

Poly(ADP-ribose) polymerase (PARP)-1 is a nuclear enzyme essential in several cellular functions such as DNA repair, DNA transcription, carcinogenesis, and apoptosis. Expression of the PARP-1 gene is mainly dictated by the transcription factor Sp1. Fibronectin (FN), a component from the extracellular matrix transiently expressed at high levels during wound healing of the corneal epithelium, was reported to exert a positive influence on expression of the alpha5 integrin subunit gene promoter by altering the state of Sp1 phosphorylation, a process that depended on the activation of the ERK signaling pathway. The present study was undertaken to investigate whether PARP-1 gene expression might be similarly regulated by FN through the same signaling pathways and attempted to link expression of this gene to corneal wound healing in vitro.

METHODS

Expression of PARP-1, Sp1/Sp3, ERK1/2, phospho-ERK1/2, P38 and phospho-P38 was monitored by Western blot in cultures of rabbit corneal epithelial cells (RCECs) grown on FN in the presence of inhibitors of the MAPK, PI3K, and P38 signaling pathways. Electrophoretic mobility shift assays (EMSAs) were conducted to assess the binding of Sp1 and Sp3 in nuclear extracts from RCECs grown on FN in the presence of inhibitors. Plasmids bearing the PARP-1 promoter fused to the CAT reporter gene were also transfected into RCECs grown under similar culture conditions to assess the influence of these inhibitors on PARP-1 promoter activity.

RESULTS

Expression of PARP-1, Sp1, and Sp3 increased considerably in RCECs grown on FN and translated into increased binding of Sp1 and Sp3 to their DNA target sites. In addition, FN increased PARP-1 promoter activity in a cell-density-dependent manner. Inhibition of both the MAPK and the PI3K pathways entirely abolished these properties.

CONCLUSIONS

PARP-1 gene expression was strongly activated by FN through alterations in the phosphorylation state of Sp1 and Sp3 that resulted from the activation of the MAPK and PI3K signaling pathways, thereby suggesting that PARP-1 may play a critical function during the highly proliferative phase that characterizes wound healing of the corneal epithelium.

Effects of the COOH-terminal tripeptide alpha-MSH(11-13) on corneal epithelial wound healing: role of nitric oxide

It is known that alpha-melanocyte stimulating hormone (alpha-MSH) may exert anti-inflammatory effects and facilitate reparative processes in different tissues. The effective message sequence of alpha-MSH resides in the COOH-terminal tripeptide alpha-MSH(11-13). This study was undertaken to investigate the effects of topical administration of the COOH-terminal tripeptide sequence of alpha-MSH (alpha-MSH(11-13), KPV) on corneal epithelial wound healing in rabbits and the possible role of nitric oxide (NO) in these effects. The whole corneal epithelium was denuded in both eyes by mechanical abrasion. The area of the corneal epithelial defect was stained with fluorescein, photographed, and then measured before the treatment and every 12 h by a computerized software. The mean epithelial wound area and the mean percent of epithelial defect remaining at each follow-up control were compared between experimental groups. Rabbits were topically treated with KPV 1, 5 or 10 mg/ml (30 microl), two drops four times in a day, for 4 days, starting immediately after corneal abrasion, while control animals received topical phosphate-buffered saline as vehicle. In order to study the role of NO in corneal repair processes, the NO donor, sodium nitroprusside (SP, 10 mg/ml, 30 microl) was administered in both eyes, two drops four times in a day, for 4 days. The effects of KPV or SP were challenged by pre-treatment with the nitric oxide synthase inhibitor, N omega-nitro-L-arginine methyl ester (L-NAME, 10 mg/ml, 30 microl) 30 min prior to KPV or SP instillation. The mean percent epithelial defect remaining each time was significantly smaller in animals treated with KPV or SP in comparison to controls. Sixty hours later, eight out of eight (100%) corneas treated with KPV or SP were completely re-epithelized (P<0.05) while none of the corneas treated with placebo were re-epithelized. Pre-treatment with L-NAME inhibited the facilitating effect of KPV on corneal epithelial wound healing process and totally prevented the effect of SP. Rabbit corneal epithelial cells (RCE) in culture were exposed for 1, 6 and 24 h to different KPV concentrations (0.1, 1 and 10 microM) in medium containing 15% foetal bovine serum (FBS). Cell viability was stimulated by 1 and 10 microM concentrations of the substance. Thus, KPV may facilitate corneal epithelial wound healing in rabbits with a mechanism that may involve NO disposition in corneal tissue. However, it is not known whether this mechanism is likely to depend on a direct stimulating repairing activity shared by the entire molecule of alpha-MSH.

The roles of calcium signaling and ERK1/2 phosphorylation in a Pax6+/- mouse model of epithelial wound-healing delay

Background

Congenital aniridia caused by heterozygousity at the PAX6 locus is associated with ocular surface disease including keratopathy. It is not clear whether the keratopathy is a direct result of reduced PAX6 gene dosage in the cornea itself, or due to recurrent corneal trauma secondary to defects such as dry eye caused by loss of PAX6 in other tissues. We investigated the hypothesis that reducing Pax6 gene dosage leads to corneal wound-healing defects. and assayed the immediate molecular responses to wounding in wild-type and mutant corneal epithelial cells.

Results

Pax6^+/- mouse corneal epithelia exhibited a 2-hour delay in their response to wounding, but subsequently the cells migrated normally to repair the wound. Both Pax6^+/+ and Pax6^+/- epithelia activated immediate wound-induced waves of intracellular calcium signaling. However, the intensity and speed of propagation of the calcium wave, mediated by release from intracellular stores, was reduced in Pax6^+/- cells. Initiation and propagation of the calcium wave could be largely decoupled, and both phases of the calcium wave responses were required for wound healing. Wounded cells phosphorylated the extracellular signal-related kinases 1/2 (phospho-ERK1/2). ERK1/2 activation was shown to be required for rapid initiation of wound healing, but had only a minor effect on the rate of cell migration in a healing epithelial sheet. Addition of exogenous epidermal growth factor (EGF) to wounded Pax6^+/- cells restored the calcium wave, increased ERK1/2 activation and restored the immediate healing response to wild-type levels.

Conclusion

The study links Pax6 deficiency to a previously overlooked wound-healing delay. It demonstrates that defective calcium signaling in Pax6^+/- cells underlies this delay, and shows that it can be pharmacologically corrected. ERK1/2 phosphorylation is required for the rapid initiation of wound healing. A model is presented whereby minor abrasions, which are quickly healed in normal corneas, transiently persist in aniridic patients, compromising the corneal stroma.

Autologous serum for the treatment of corneal epithelial abrasions in diabetic patients undergoing vitrectomy

PURPOSE

To compare the effect of autologous serum versus hyaluronic acid for the treatment of epithelial corneal lesions in patients such as diabetics with reduced wound healing.

DESIGN

Prospective, randomized, masked clinical trial.

METHODS

Diabetic patients undergoing pars plana vitrectomy mostly combined with cataract extraction and intraocular lens (IOL) implantation who received corneal abrasion for better intraoperative visualization were included in this study. A standardized 8-mm diameter corneal abrasion was performed. Patients were randomized into one group treated with hourly application of autologous serum and another treated with hyaluronic acid drops (Vislube). Besides the time necessary for closure of the corneal epithelium other parameters such as patients' age, gender, duration of surgery, history of diabetes, and current HbA1C were evaluated.

RESULTS

A total of 23 patients were enrolled (15 men, eight women); the autologous serum group consisted of 13 patients, the hyaluronic acid (Vislube) group consisted of 10 patients. Patients' mean age was 64.8 years; mean duration of diabetes was 19.4 years. On average, the operation lasted 145 minutes. Mean epithelialization time was 7.1 days in the hyaluronic acid group. In the autologous serum group, epithelium healed after a mean of 4.3 days. Mann-Whitney U test for statistical analysis showed a significant difference of epithelial closure time between both groups (P < .05); therefore, the study was stopped after treatment of 23 patients.

CONCLUSIONS

It appears that autologous serum leads to a much faster closure of corneal epithelial wounds after abrasion compared with artificial tears.

Two waves of neutrophil emigration in response to corneal epithelial abrasion: distinct adhesion molecule requirements

PURPOSE

Corneal abrasion results in an inflammatory response characterized by leukocyte emigration into the corneal stroma. Adhesion molecules play a critical role in leukocyte emigration to wound sites, but differences are evident in different vascular beds. In this study, the contributions of two families of adhesion molecules to neutrophil emigration into the cornea were investigated.

METHODS

Re-epithelialization, patterns of neutrophil influx and CXC chemokine production were assessed in C57Bl/6 mice after removal of a 2-mm diameter area of central corneal epithelium. Comparisons were made between wild-type (WT) mice and mice with targeted deletions of genes for CD18 (CD18(-/-)) or P- and E-selectin (P/E-sel(-/-)) or in mice with antibody-induced neutropenia.

RESULTS

Wild-type mice exhibited neutrophil emigration in two waves, the first peaking at 18 hours and the second at 30 hours after wounding, 6 hours after epithelial wound closure and peak levels of corneal CXCL1. In CD18(-/-) animals, only a single wave of neutrophil influx was seen, and it was temporally and quantitatively equivalent to the second wave in WT. In P/E-sel(-/-) mice, neutrophil influx was markedly depressed throughout the 48-hour observation period. Re-epithelialization was significantly delayed in mice with adhesion molecule deletions and in neutropenic animals. Transfer of wild-type leukocytes into CD18(-/-) mice resulted in neutrophil emigration into the injured cornea within 18 hours of wounding and improved closure of the epithelium.

CONCLUSIONS

Neutrophil emigration into corneal stroma after epithelial abrasion occurs in two waves. The first is dependent on CD18 integrins and selectins, whereas the second is CD18-independent but requires selectins. Early leukocyte emigration appears to promote re-epithelialization.

Promotion of corneal epithelial wound healing in vitro and in vivo by annexin A5

PURPOSE

To investigate the effect of annexin A5, a calcium-dependent phospholipid-binding protein, on corneal epithelial wound healing.

METHODS

The effect of annexin A5 on migration of rabbit corneal epithelial (RCE) cells in vitro was examined in scrape-wounded cell monolayers. The effect of annexin A5 on the release of urokinase-type plasminogen activator (uPA) from cultured RCE cells was determined by zymography, fluorogenic assay of PA activity, and enzyme-linked immunosorbent assay. The proliferation of RCE cells was assessed by measurement of [3H]thymidine incorporation. The effect of annexin A5 on corneal wound closure in rabbits was investigated after removal of the corneal epithelium, either by exposure to iodine vapor or surgically. Eye drops containing annexin A5 were instilled into one eye and vehicle into the other. The area of the epithelial defect was measured at various times after wounding, and the healing rate was calculated by linear regression analysis.

RESULTS

Annexin A5 significantly promoted the migration of RCE cells in a wounded monolayer. However, annexin A5 had no effect on RCE cell proliferation. Annexin A5 also increased the release of uPA both from wounded RCE cell monolayers and from nonwounded semiconfluent RCE cells. In both models of corneal wound closure, the healing rate was significantly increased by instillation of eye drops containing annexin A5 compared with that apparent in the eyes that received vehicle.

CONCLUSIONS

Annexin A5 promoted corneal epithelial wound healing both in vitro and in vivo. Upregulation of uPA release from corneal epithelial cells may contribute to this effect of annexin A5.

Effects of the matrix metalloproteinase inhibitor GM6001 on the destruction and alteration of epithelial basement membrane during the healing of post-alkali burn in rabbit cornea

PURPOSE

To examine the alteration in structure and matrix composition of epithelial basement membrane (BM) during the healing of alkali-burned rabbit cornea, and the roles of matrix metalloproteinases (MMPs) in these alterations.

METHODS

The central cornea of one eye of 78 albino rabbits was exposed to 1 N NaOH for 180 s under general and topical anesthesia and allowed to heal with or without subconjunctival injection of GM6001 (an MMP inhibitor). Cryosections of affected corneas were observed by H&E staining, immunohistochemistry for type IV collagen subtypes, or in situ zymography for detection of localization of MMP activity.

RESULTS

Uninjured corneal epithelial BM exhibited alpha5 (IV)-immunoreactivity, but lacked the alpha1/alpha2-immunoreactivity of collagen IV. Epithelial BM in healing burned cornea transiently exhibited alpha1/alpha2-immunoreactivity. Examination by in situ zymography showed an upregulation of MMP activity in the regenerated central epithelium and anterior stroma of the burned corneas at days 7 and 14. GM6001 suppressed degradation of alpha5-containing epithelial BM in vivo and also in organ culture.

CONCLUSIONS

Epithelial BM was degraded by endogenous MMPs during healing following an alkali burn in rabbit cornea. GM6001 had an inhibitory effect on the degradation of the epithelial basement membrane in burned cornea in vivo.

Traumatic epithelial flap detachment after laser subepithelial keratomileusis

PURPOSE

To report a case of corneal epithelial flap detachment 20 days after laser subepithelial keratomileusis (LASEK).

METHODS

A 30-year-old man underwent LASEK for correction of myopia. On postoperative day 8, he was comfortable and the corneal epithelium healed completely with uncorrected visual acuity (UCVA) of 20/20. On postoperative day 20, the corneal epithelial flap on the right eye detached and was lost during pressure patching after puncture of the hordeolum.

RESULTS

The corneal defect was treated with a bandage contact lens, levofloxacin, and hyaluronic acid eye drops. Ten days after detachment, UCVA had improved to 20/20 and the epithelium had closed completely.

CONCLUSIONS

Mild trauma can cause epithelial flap detachment during the early postoperative period of LASEK.

The cleavage plane of corneal epithelial adhesion complex in traumatic recurrent corneal erosion

PURPOSE

To determine the anatomic cleavage plane of the corneal epithelial adhesion complex in eyes with traumatic recurrent corneal erosion (RCE).

METHODS

A loosened sheet of corneal epithelium was obtained from corneal epithelial wounds in eight patients with traumatic RCE, before each patient underwent phototherapeutic keratectomy. Three control groups were employed in the study, including normal corneal epithelial sheets obtained by mechanical separation, normal corneal tissues obtained by partial lamellar keratectomy during pterygial surgery, and corneal tissues from three residual corneoscleral rims of corneas donated for transplantation. Immunofluorescence staining was performed using monoclonal antibodies against integrins beta1 and beta4, laminin 5, and collagen VII to identify abnormalities in specific layers of the adhesion complex.

RESULTS

In both experimental and control specimens, the suprabasal and basal cells stained positive for integrin beta1, and basal cells stained positive for integrin beta4. Similarly, a continuous line along the base of each epithelial sheet and each control specimen stained positive for laminin 5, a major basement membrane component. In contrast, in all controls there was a continuous linear staining pattern along the basement membrane of stain positive for collagen VII, a marker for the presence of fibrils that anchor corneal basement membrane to Bowman's layer, but epithelial sheets from eyes with RCE showed either a discontinuous line stained positive for collagen VII (three out of eight specimens) or no positively stained areas (five out of eight specimens). The results indicated the cleavage plane of RCE was located at collagen VII layer, between basement membrane and Bowman's layer.

CONCLUSIONS

This study identified a defect in collagen fibrils that anchor the corneal epithelium basement membrane to Bowman's layer as the cause of corneal epithelial loss in cases of traumatic RCE. As hemidesmosomes do not seem to be impaired, a treatment specific to restore anchoring fibril function might prove helpful.

Corneal deposits and topical ofloxacin—the effect of polypharmacy in the management of microbial keratitis

PURPOSE

To report six cases of corneal deposits after administration of topical ofloxacin in the treatment of bacterial keratitis.

METHOD/RESULT

Six cases of microbial keratitis treated with multiple topical medications, including topical ofloxacin, resulted in corneal precipitates and poor wound healing. In five cases, the precipitates resolved with discontinuation of ofloxacin treatment. However, in one patient, some residual deposits persisted following discontinuation of ofloxacin. The cornea epithelialised, but deposits were identified subepithelially.

DISCUSSION

Fluoroquinolone antibiotic drops have been extensively used in bacterial keratitis because of their ease of availability, broad spectrum of activity, and lack of toxicity. While corneal precipitates have been reported with cases of topical ciprofloxacin and norfloxacin, little has been documented on corneal deposits and topical ofloxacin in the treatment of bacterial keratitis. The predisposing factors resulting in corneal deposits and the role of polypharmacy are important features that may impair epithelialisation. Clinical management should be aimed at reducing the toxic environment and promoting ocular surface stability.

Expression of keratin 12 and maturation of corneal epithelium during development and postnatal growth

PURPOSE

To determine the kinetics of corneal epithelial maturation during embryonic development and postnatal growth.

METHODS

Expression patterns of keratin (K)12 and K14 were determined in mouse embryos (embryonic days [E]15.5-19.5), corneas of postnatal day (P)0 to 10 months, and healing corneas after epithelial debridement in P30 and P90 mice. The expression of alkaline phosphatase (AP) was determined during postnatal growth and healing of epithelial debridement of Krt12(Cre/Cre)/ZAP bitransgenic mice.

RESULTS

During embryonic development, K12 expression by corneal peridermal epithelium commenced at E15.5. In the period from E15.5 to P10, the expression of K12 was restricted to the suprabasal and/or superficial cells of the corneal epithelium, whereas the K14 expression was restricted to the basal cells. After P30, K12 expression was sporadically detected in the basal corneal epithelium, and the number of K12-positive basal cells increased as the mice grew older. The number of K14-positive cells that coexpressed K12 increased with age and reached a plateau after P180. Healing of the debrided epithelium facilitated the increase in K14-positive cells that coexpressed K12. Many basal cells of Krt12(Cre/Cre)/ZAP mice remained undifferentiated and expressed LacZ at P15, and they then differentiated to express Cre, which leads to excision of LacZ and AP expression.

CONCLUSIONS

In the mouse, the corneal epithelium does not become fully mature until 3 to 6 months after birth, in that a significant number of corneal basal epithelial cells of young mice (<P30), which derive from embryonic surface ectoderm remain undifferentiated and serve as corneal epithelial progenitor cells. These progenitor cells may have some stem cell characteristics.

Long-term Refractive Results of Myopic LASIK Complicated With Intraoperative Epithelial Defects

PURPOSE

To evaluate the long-term refractive results of LASIK for myopia complicated with intraoperative epithelial defects.

METHODS

Twenty-six eyes with epithelial defects on the LASIK flap were compared with the contralateral eye that had no intraoperative complications. Pre- and postoperative data were compared between the two groups including 3-, 6- and 12-month postoperative spherical equivalent refraction, amount of undercorrection, and complications.

RESULTS

Eyes with intraoperative epithelial defects showed more undercorrection at 3 and 6 months postoperatively (P < .05). No statistically significant difference was noted at 12 months. Twenty (76%) eyes in the epithelial defect group lost best spectacle-corrected visual acuity (BSCVA) at 3 months postoperatively compared with 2 (7%) eyes in the control group. By 1 year, however, only 2 (7%) eyes in the epithelial defect group and no eyes in the control group lost > 1 line of BSCVA. Diffuse lamellar keratitis was observed in 15 (58%) of 26 eyes with epithelial defects and these eyes had more undercorrections at 6 and 12 months (P < .05) and higher corneal irregularity index at 6 and 12 months compared with controls (P < .05). Eyes with small epithelial defects (> 1 mm2 to < 3 mm2) had more undercorrections at 6 months (-1.08 +/- 0.76 diopters [D]) compared with the control group (-0.46 +/- 0.87 D). Eyes with centrally located epithelial defects had more undercorrections and increased corneal irregularity index compared with controls (P < .05).

CONCLUSIONS

Intraoperative epithelial defects after LASIK should be considered a severe complication that may result in diffuse lamellar keratitis, induce loss of BSCVA, prolong recovery of visual acuity, and induce undercorrection.