Gefarnate stimulates secretion of mucin-like glycoproteins by corneal epithelium in vitro and protects corneal epithelium from desiccation in vivo

Is the main lacrimal gland indispensable? Contributions of the corneal and conjunctival epithelia

The ocular surface system is responsible for ensuring that the precorneal tear film is sufficient in both quality and quantity to preserve optimal vision. Tear secretion is a complex, multifactorial process, and dysfunction of any component of the ocular surface system can result in tear film instability and hyperosmolarity with resultant dry eye disease. The tear film is primarily composed of lipids, aqueous, and mucins, with aqueous accounting for most of its thickness. The aqueous is produced by the main lacrimal gland, accessory lacrimal glands, and corneal and conjunctival epithelia. Although the main lacrimal gland has long been considered an indispensable source of the aqueous component of tears, there is evidence that adequate tear secretion can exist in the absence of the main lacrimal gland. We review and discuss the basics of tear secretion, the tear secretory capacity of the ocular surface, and emerging treatments for dry eye disease.

Perforating corneal injury in rat and pentadecapeptide BPC 157

Based on its healing effects in various tissues, we hypothesized that the stable gastric pentadecapeptide BPC 157 heals corneal ulcerations in rats and effects corneal transparency. We made a penetrant linear 2-mm incision in the paralimbal region of the left cornea at the 5 o'clock position with a 20-gauge MVR incision knife at 45° under an operating microscope. Medication was BPC 157 (2 pg/mL, 2 ng/mL, and 2 μg/mL distilled water, two eye drops/left rat eye) immediately after injury induction and then every 8 h up to 120 h; controls received an equal volume of distilled water. In contrast to the poor healing response in controls, BPC 157 significantly accelerated the healing process in 2 μg and 2 ng BPC 157-treated eyes, starting 24 h after the injury, and the fluorescein and Seidel tests became negative. The epithelial defects were completely healed at 72 h (2 μg BPC 157-treated group) and at 96 h (2 ng BPC 157-treated group) after injury. Aqueous cells were absent at 96 h and 120 h after injury in the 2 μg and 2 ng BPC 157-treated groups, respectively. In conclusion, BPC 157 effects the rapid regaining of corneal transparency. Whereas controls developed new vessels that grew from the limbus to the penetrated area, BPC 157-treated rats generally had no new vessels, and those that did form in the limbus did not make contact with the penetrated area. Thus, BPC 157 eye drops successfully close perforating corneal incisions in rats.

Regulation of human corneal epithelial mucins by rebamipide

PURPOSE

Membrane-associated mucins (MAMs) play important roles in barrier function and tear stability, and their expression on the ocular surface is altered in dry eye disease. Rebamipide is a mucin secretagogue that promotes the production of mucin-like glycoproteins in human corneal epithelial (HCE) cells. However, the expression of MAMs on the corneal epithelia (MUC1, MUC4, MUC16), which is induced by rebamipide, is poorly understood. In this study, we investigated the effect of rebamipide on the regulation of MAM expression in HCE cells.

MATERIALS AND METHODS

MUC16, Ki67 and PCNA expression levels in HCE cells isolated at confluence and at 24 hours after confluence were examined by Western blotting to assess cell proliferation. HCE cells isolated at 24 hours after confluence were cultured in medium supplemented with 1-10 µM rebamipide or 0.3-30 nM of epidermal growth factor (EGF). Real-time PCR (RT-PCR) and Western blot analysis of MAMs were performed to evaluate the effect of rebamipide. Western blot analysis of cells treated with an EGF receptor inhibitor (AG1478) or MEK1/2 inhibitor (U0126) was performed to reveal the relationship between EGF receptor activation and rebamipide-induced MAM expression.

RESULTS

HCE cells isolated at 24 hours after confluence had lower cell proliferation activity and increased MUC16 expression compared with cells isolated at confluence. RT-PCR and Western blot analysis revealed that rebamipide increased MAM gene expression for 2 hours and protein expression for 24 hours in HCE cells. EGF inhibitor treatment led to reduced levels of all three MAMs that are normally induced by rebamipide, whereas EGF induced the expression of all three MAMs.

CONCLUSIONS

We suggested that rebamipide increased MUC1, MUC4 and MUC16 expression levels through signals involved in EGF receptor activation in the human corneal epithelia. These data suggest that rebamipide may improve subjective symptoms of dry eye disease by upregulating MAM expression.

Gefarnate stimulates mucin-like glycoprotein secretion in conjunctival tissue and ameliorates corneal epithelial damage in animal dry-eye models

Purpose

The aim of this study was to evaluate the effect of gefarnate on mucin-like glycoprotein secretion in isolated rabbit conjunctival tissue, and on corneal epithelial damage in rabbit and cat dry-eye models.

Methods

Conjunctival tissue isolated from rabbits was treated with gefarnate. Mucin-like glycoprotein was detected in the culture supernatant by an enzyme-linked lectin assay. Gefarnate ointment was topically applied to eyes once daily for 7 days in the rabbit dry-eye model, in which the lacrimal glands, Harderian gland, and nictitating membrane were removed, or for 4 weeks in the cat dry-eye model, in which the lacrimal gland and nictitating membrane were removed. Corneal epithelial damage was evaluated by measurement of corneal permeability by rose bengal in the rabbit model or by fluorescein staining in the cat model.

Results

Gefarnate stimulated mucin-like glycoprotein secretion in conjunctival tissue in a dose-dependent manner. In the rabbit dry-eye model, application of gefarnate ointment to the eyes resulted in a dose-dependent decrease in rose bengal permeability in the cornea, with the effect being significant at concentrations of ≥0.3%. In the cat dry-eye model, application of gefarnate ointment resulted in a significant decrease in the corneal fluorescein staining score.

Conclusion

These results suggest that gefarnate stimulates in vitro secretion of mucin-like glycoprotein in conjunctival tissue and ameliorates corneal epithelial damage in animal dry-eye models. Gefarnate may therefore be effective for treating dry eye.

Efficacy of retinol palmitate eye drops for dry eye in rabbits with lacrimal gland resection

Purpose

We examined the efficacy of retinol palmitate (VApal) for dry eyes using dry eye model rabbits whose lacrimal glands were resected.

Materials and methods

After alkaline injury on keratoconjunctival epithelium, VApal eye drops were administered 6 times a day for 7 days. The efficacy of VApal was also compared with that of 0.1% hyaluronic acid eye drops.

Results

The fluorescein staining and rose bengal scores showed a significant decrease compared with the score in the vehicle group at 7 days (P < 0.05) in the 1000 IU/mL VApal group and at both 3 days (P < 0.05) and 7 days (P < 0.01) in the 1500 IU/mL VApal group. Histological examination revealed recovery of the corneal epithelium, and PAS staining disclosed the recovery of mucin-producing lower palpebral conjunctival goblet cells after 7 days in the 1500 IU/mL VApal group compared with the vehicle group. Results from impression cytology showed a significant increase in density of conjunctival goblet cells compared with that in the vehicle group after 7 days in the 1000 IU/mL VApal group and after 3 and 7 days in the 1500 IU/mL VApal group. There were no significant changes in tear flow in either group. Topical application of VApal at 1500 IU/mL showed greater improvement than 0.1% hyaluronic acid in both fluorescein and rose bengal score and in the density of conjunctival goblet cells.

Conclusion

It is suggested that VApal is effective for the improvement of keratoconjunctival epithelial damage associated with tear abnormalities, such as dry eyes.

Rebamipide increases mucin-like substance contents and periodic acid Schiff reagent-positive cells density in normal rabbits

PURPOSE

The effects of rebamipide on the number of periodic acid Schiff reagent (PAS)-positive cells in the conjunctiva, the mucin content in the cornea and conjunctiva of normal rabbits, and desiccation-induced corneal damage in vivo were examined.

METHODS

Rebamipide (0.1%-3%) was applied 6 times a day for 14 days, and the PAS-positive cell count in the bulbar conjunctiva was measured by impression cytology. The amount of conjunctival and corneal mucin-like substances was measured by Alcian blue binding. The corneal damage model was created by desiccation from air flow at room temperature. The level of corneal damage was determined by scoring the area stained with rose bengal and fluorescein dye.

RESULTS

Rebamipide increased the number of PAS-positive cells in the conjunctiva when instilled at concentrations of 0.3% or higher, and 1% rebamipide increased the amount of mucin-like substances of the conjunctiva and cornea. Moreover, 1% rebamipide was also found to lower the rose bengal scores of the cornea in the corneal damage model by desiccation.

CONCLUSIONS

Rebamipide is a possible candidate drug for treatment of cornea and conjunctival epithelial damage due to its mucin-like substance increasing action, for instance, in the treatment of dry eye disease.

Character of ocular surface mucins and their alteration in dry eye disease

At the ocular surface, three types of mucins are present. The large gel-forming mucin MUC5AC is expressed by conjunctival goblet cells. Some cells of the lacrimal gland acini express the small soluble mucin MUC7. The corneal and conjunctival epithelia express the membrane-associated mucins MUCs 1, 4, and 16. With the characterization of the mucin gene repertoire of the ocular surface epithelia, studies of the function of specific mucins, their gene regulation, and their alteration in ocular surface disease have begun. Current information suggests that all the mucins are hydrophilic and play a role in maintenance of water on the surface of the eye. The large secreted mucins represent the "janitorial service" that moves over the surface of the eye to wrap up and remove debris. The membrane-associated mucins form the glycocalyx, which provides a continuous barrier across the surface of the eye that prevents pathogen penetrance and has signaling capabilities that influence epithelial activity. Factors regulating mucin gene expression include retinoic acid, serum, and dexamethasone. Alteration in both secreted and membrane-associated mucins occur in drying ocular surface diseases. In Sjogren syndrome, MUC5AC expression is reduced, and in non-Sjogren dry eye, glycosylation of MUC16 appears to be altered. The pattern of expression of enzymes that glycosylate mucins is altered in ocular cicatricial pemphigoid. Therapies being evaluated for dry eye, including cyclosporine A, P2Y2 agonists, gefarnate, 15-(S)-HETE, and corticosteroids, may be efficacious due to their effect on mucin gene expression and secretion.

Primary Sjogren's syndrome: current and prospective therapies

OBJECTIVE

To summarize data on existing and experimental therapies for primary Sjogren's syndrome (pSS), referring both to sicca syndrome and to other systemic disease manifestations.

METHODS

Relevant English and non-English articles acquired through Medline were reviewed.

RESULTS

pSS usually has a benign clinical course, centered on sicca features and general musculoskeletal manifestations, and is managed symptomatically. However, a subset of patients develops more severe extraglandular disease that warrants close monitoring and aggressive treatment. For dry eyes and mouth, nonpharmacologic measures to preserve secretions, and tear and saliva substitutes, offer some symptomatic relief. Muscarinic agonists and topical cyclosporine yield well-documented improvement in ocular sicca features. Although traditional antirheumatic drugs are used empirically for polyarthritis and other Sjogren's symptoms, their efficacy in pSS overall and as disease-modifying agents is limited. For the potential severe, nonexocrine manifestations complicating pSS, standard high-dose immunosuppression is used. Among the biologic agents already examined in pSS, those targeting tumor necrosis factor (TNF)-alpha failed to demonstrate significant benefit. Nonetheless, rituximab and other B-cell-depleting therapies appear promising.

CONCLUSIONS

Treatment of pSS patients with severe extraglandular disease should differ from that of patients with predominantly sicca features and/or general muscoloskeletal manifestations. pSS treatment is mainly symptomatic, primarily directed against sicca complaints. The traditional anti-rheumatic agents show limited efficacy in the systemic process and use of systemic TNF-alpha inhibitors has been very disappointing. B cell depleting treatments and other newer biologic therapies appear more promising.

Management and Therapy of Dry Eye Disease: Report of the Management and Therapy Subcommittee of the International Dry Eye WorkShop (2007)

The members of the Management and Therapy Subcommittee assessed current dry eye therapies. Each member wrote a succinct evidence-based review on an assigned aspect of the topic, and the final report was written after review by and with consensus of all subcommittee members and the entire Dry Eye WorkShop membership. In addition to its own review of the literature, the Subcommittee reviewed the Dry Eye Preferred Practice Patterns of the American Academy of Ophthalmology and the International Task Force (ITF) Delphi Panel on Dry Eye. The Subcommittee favored the approach taken by the ITF, whose recommended treatments were based on level of disease severity. the recommendations of the Subcommittee are based on a modification of the ITF severity grading scheme, and suggested treatments were chosen from a menu of therapies for which evidence of therapeutic effect had been presented.

Design and Conduct of Clinical Trials: Report of the Clinical Trials Subcommittee of the International Dry Eye WorkShop (2007)

This report summarizes some universal concepts with regard to clinical trials in general and other issues pertaining to clinical trials specifically tailored to the study of therapeutic intervention in dry eye disease. The report also makes recommendations for logistical design and implementation of such trials. It identifies peculiarities of dry eye disease that complicate clinical trial design, such as the lack of correlation of signs and symptoms, as well as the likelihood of control interventions having a lubricant (placebo) effect. Strategies for environmental trials and controlled adverse environment trials are reviewed.

Changes in the tear film and ocular surface from dry eye syndrome

Dry eye syndrome (DES) refers to a spectrum of ocular surface diseases with diverse and frequently multiple aetiologies. The common feature of the various manifestations of DES is an abnormal tear film. Tear film abnormalities associated with DES are tear deficiency, owing to insufficient supply or excessive loss, and anomalous tear composition. These categorizations are artificial, as in reality both often coexist. DES disrupts the homeostasis of the tear film with its adjacent structures, and adversely affects its ability to perform essential functions such as supporting the ocular surface epithelium and preventing microbial invasion. In addition, whatever the initial trigger, moderate and severe DES is characterized by ocular surface inflammation, which in turn becomes the cause and consequence of cell damage, creating a self-perpetuating cycle of deterioration. Progress has been made in our understanding of the aetiology and pathogenesis of DES, and these advances have encouraged a proliferation of therapeutic options. This article aims to amalgamate prevailing ideas of DES development, and to assist in that, relevant aspects of the structure, function, and production of the tear film are reviewed. Additionally, a synopsis of therapeutic strategies for DES is presented, detailing treatments currently available, and those in development.

Corneal protection by the ocular mucin secretagogue 15(S)-HETE in a rabbit model of desiccation-induced corneal defect

The mucin secretagogue 15(S)-HETE was found to stimulate glycoprotein secretion in human ocular tissue at submicromolar concentrations in the present studies. Therefore, the ability of topically applied 15(S)-HETE to preserve corneal integrity was investigated in a rabbit model of desiccation-induced corneal defect. Desiccation-induced corneal injury was elicited in anesthetized rabbits by maintaining one eye open with a speculum. Corneal staining and corneal thickness changes were determined immediately following desiccation. 15(S)-HETE dose-dependently reduced corneal damage (ED50 = 120 nM) during a two-hour desiccation. Corneal staining was unchanged relative to control using a 1 microM dose of 15(S)-HETE. Through four hours of desiccation, 15(S)-HETE (500 nM) decreased corneal staining by 71% and completely prevented corneal thinning. 15(S)-HETE (1 microM) was significantly more efficacious than an artificial tear product over the 4-hour desiccation period. There was no evidence of tachyphylaxis following repeated topical ocular dosing of 15(S)-HETE. These studies demonstrate that 15(S)-HETE stimulates ocular mucin secretion in vitro and effectively protects the cornea in a rabbit model of desiccation-induced injury. The results suggest that the ocular mucin secretagogue 15(S)-HETE may have therapeutic utility in dry eye patients, alleviating corneal injury and restoring corneal integrity.

INS365 suppresses loss of corneal epithelial integrity by secretion of mucin-like glycoprotein in a rabbit short-term dry eye model

P2Y2 receptor agonists, like UTP and ATP, stimulate mucin secretion from goblet cells in vitro. Therefore, mucin stimulants could be good candidates for the treatment of dry eye syndrome because mucin increases the tear film stability and protects against desiccation of ocular surface. INS365 is a more stable P2Y2 receptor agonist than UTP. In the present study, we evaluated, in normal rabbit eyes, its effectiveness to release mucin from goblet cells and to protect the corneal damage induced by desiccation. For mucin secretion, impression cytology was performed following the instillation of INS365 solution or saline into the conjunctival sac. The specimens were stained with periodic acid and Schiff (PAS) reagent, and then the staining area was calculated using computer software. INS365 dose-dependently decreased the PAS staining area of conjunctival goblet cells from 2 to 15 min post-application. Furthermore, we utilized the rabbit short-term dry eye model to evaluate if INS365 eyedrops could protect against any of the damage produced by blockage of blinking with ocular speculum. INS365 significantly suppressed corneal damage at concentrations of more than 0.1% w/v. These results suggest that this P2Y2 agonist is a good candidate for the treatment of dry eye disease.

Effect of gefarnate on the ocular surface in squirrel monkeys

PURPOSE

To investigate the ability of gefarnate (geranyl farnesylacetate) to stimulate goblet cell function in the primate eye after a mild alkali injury of the tarsal conjunctiva.

METHODS

A bilateral injury was created on the conjunctival surface of the lower eye lid of squirrel monkeys by means of a 30-second application of a 4-mm diameter piece of filter paper wetted with 0.5% NaOH. Gefarnate drops (1%) were administered to one eye of each monkey and vehicle alone in the contralateral eye six times a day, 5 days a week for 4 weeks. Slit-lamp biomicroscopy, impression cytology staining of the ocular surface, fluorescein and rose bengal staining, and Western blot for mucin were performed before injury and weekly thereafter. Light microscopy was used to evaluate the lower conjunctiva.

RESULTS

Topical application of gefarnate was not associated with any adverse ocular surface effects. Goblet cell repopulation after injury was significantly greater in the gefarnate-treated eyes compared with the vehicle-treated eyes. In the gefarnate-treated eyes, tear mucin content was significantly greater at 1 week after injury. Fluorescein staining was significantly reduced at 3 weeks after injury, and rose bengal staining was significantly reduced in the area of the wound at 2 weeks in the gefarnate-treated eyes compared with the vehicle-treated eyes; at other times, conjunctival staining in the two groups of eyes was not significantly different.

CONCLUSIONS

Gefarnate promotes goblet cell repopulation and increases mucin production after a conjunctival injury. No adverse affects of the treatment were found. Thus, this agent may be useful in conditions that diminish goblet cell function.

The eicosanoid, 15-(S)-HETE, stimulates secretion of mucin-like glycoprotein by the corneal epithelium

PURPOSE

The eicosanoid, 15-(S)-hydroxyeicosa-5Z, 8Z-11Z, 13E-tetraenoic acid (15-(S)-HETE), is known to stimulate production of mucin glycoprotein by airway epithelium. This study investigated the effect of 15-(S)-HETE on the mucin glycoprotein secretion by the corneal epithelium.

METHODS

To determine the effect of dose, corneas of anesthetized New Zealand White rabbits were treated with 50, 500, or 5,000 nM 15-(S)-HETE in artificial tears for 120 minutes. To determine the time to onset of the response, corneas were treated with 500 or 1,000 nM 15-(S)-HETE in balanced salt solution for periods ranging from 5 to 120 minutes. Corneas were fixed for electron microscopy in fixative containing 0.5% cetylpyridinium chloride (CPC) to stabilize the layer of mucin-like glycoprotein on the corneal surface. The mucin layer thickness was measured by image analysis of electron micrographs.

RESULTS

The layer of CPC-fixed mucin-like glycoprotein on the surface of control corneas was 0.46 +/- 0.04 microm thick. After treatment with 15-(S)-HETE, the thickness of the mucin layer increased to 0.64 +/- 0.1 microm at 50 or 5,000 nM HETE and as much as 1.02 +/- 0.2 microm in response to 500 nM HETE. Mucin thickness reached a statistical maximum of 0.59 +/- 0.1 microm after only 5 minutes of exposure to 500 or 1,000 nM HETE.

CONCLUSIONS

Exposure of the cornea to 15-(S)-HETE causes a rapid-onset increase in the thickness of a layer of mucin-like glycoprotein on the surface of the corneal epithelium. This supports previous reports that corneal epithelial cells produce mucin and suggests that treatment with topical 15-(S)-HETE may be effective in treating ocular surface mucin deficiency in dry eye syndrome.

Gefarnate increases PAS positive cell density in rabbit conjunctiva

AIMS

The effects of three drugs for the treatment of gastritis and gastric ulcer--gefarnate, ecabet sodium, and troxipide--on periodic acid Schiff (PAS) positive cell density in rabbit conjunctiva in vivo were investigated.

METHODS

Eye drops containing gefarnate (0.1%, 1%), ecabet sodium (0.1%, 1%), or troxipide (0.1%, 1%) were instilled in both eyes of rabbits, six times a day for 7 days. On the eighth day, filter paper was gently pressed on the bulbar and palpebral conjunctiva, and impression cytology was performed with PAS staining. Three points in each specimen were selected randomly, and PAS stained cells were counted.

RESULTS

The instillation of gefarnate increased PAS positive cell density significantly at the concentration of 1% (p < 0.05). In contrast, instillation of ecabet sodium or troxipide failed to change PAS positive cell density.

CONCLUSIONS

These results demonstrated that gefarnate stimulates PAS positive cell density in rabbit conjunctiva.