Establishment of a rabbit short-term dry eye model

Application of Animal Models in Interpreting Dry Eye Disease

Different pathophysiologic mechanisms are involved in the initiation, development, and outcome of dry eye disease (DED). Animal models have proven valuable and efficient in establishing ocular surface microenvironments that mimic humans, thus enabling better understanding of the pathogenesis. Several dry eye animal models, including lacrimal secretion insufficiency, evaporation, neuronal dysfunction, and environmental stress models, are related to different etiological factors. Other models may be categorized as having a multifactorial DED. In addition, there are variations in the methodological classification, including surgical lacrimal gland removal, drug-induced models, irradiation impairment, autoimmune antibody-induced models, and transgenic animals. The aforementioned models may manifest varying degrees of severity or specific pathophysiological mechanisms that contribute to the complexity of DED. This review aimed to summarize various dry eye animal models and evaluate their respective characteristics to improve our understanding of the underlying mechanism and identify therapeutic prospects for clinical purposes.

Corneal protective effects of novel tear substitutes containing sodium hyaluronate and dodecahydrosqualene, squalane, in a porcine dry eye model

To develop a novel tear substitute (TS) containing sodium hyaluronate (SH) and dodecahydrosqualene (DHS, squalane), we improved the prescription of a previously developed TS containing saline, 0.5% SH and 1% castor oil (CO), which had corneal protective effects against 60-min desiccation in a porcine dry eye model and viscosity of 106.8 mPa·S. Fresh porcine eyes were treated with a TS containing saline, 0.1%, 0.25%, 0.3% or 0.5% SH, and 1% CO or 1%, 2.5% or 5% DHS, and TS-treated eyes were desiccated for up to 180 min. The corneal damage was evaluated by the staining score of methylene blue (MB), absorbance of MB extracted from the cornea, the staining density of lissamine green (LG) and histopathology. The viscosities of the examined TS were also measured. A saline/0.5% SH/1% DHS solution had corneal protective effects for 90 min under desiccation and a viscosity of 110.0 mPa·s. A TS with saline, 0.1%, 0.25% or 0.3% SH and 1% or 2.5% DHS did not have better protective effects than a saline/0.5% SH/1% DHS solution, although a saline/0.3% SH/5% DHS solution exhibited greater corneal protection against 180-min desiccation on MB and LG staining and histopathological examination, and its viscosity was 34.5 mPa·s, which was similar to the 29.5 mPa·s of 0.3% SH. The saline/0.3% SH/5% DHS solution is available as a novel 3-hr long-lasting TS containing mucinomimetic and liquid oil components to treat and relieve dry eye symptoms in animals and humans.

Animal models of dry eye disease: Useful, varied and evolving (Review)

Dry eye disease (DED), which is a prevalent disease that still lacks successful treatment options, remains a major challenge in ophthalmology. Multiple animal models of DED have been used to decipher its pathophysiology and to develop novel treatments. These models use mice, rats, rabbits, cats, dogs and non-human primates. Each model assesses aspects of DED by focusing on elements of the lacrimal functional unit, which controls the homeostasis of the tear film. The present review outlines representative DED animal models and assesses their contribution to the study of DED. Murine models are the most extensively used, followed by rabbit models; the latter offer the advantage of larger eyes, a favorable biochemical profile for drug studies, experimental ease and relatively low cost, contrasting with non-human primates, which, although closer to humans, are not as accessible and are expensive. No comprehensive ‘ideal’ animal model encompassing all aspects of human DED exists nor is it feasible. Investigators often choose an animal model based on their experimental needs and the following four features of a given model: The size of the eye, its biochemical composition, the available research reagents and cost. As research efforts in DED expand, more refined animal models are needed to supplement the enormous contribution made to date by existing models.

A Novel Rabbit Dry Eye Model Induced by a Controlled Drying System

Purpose

To establish an environment-induced dry eye model in rabbits using a controlled drying system (CDS).

Methods

Rabbits were randomly divided into two groups. The rabbits in the dry group were housed in the CDS, in which the relative humidity, airflow, and temperature were controlled at 22% ± 4%, 3 to 4 m/s, and 23°C to 25°C for 14 days. The rabbits in the control group were housed in a normal environment at the same time. A Schirmer test, fluorescein staining, and lissamine green staining were performed. On day 14, the eyeballs and lacrimal glands were processed for evaluating the corneal epithelial thickness, inflammatory cell infiltration index, goblet cell density, and expression of the MUC5AC protein and caspase-3 protein. The mRNA expression of the involved inflammatory genes was analyzed.

Results

The CDS was able to maintain a dry environment, in which the tear production decreased, and the ocular surface staining increased over time in the rabbits. In the dry group, the corneal epithelium became thinner, inflammatory cells were noted, goblet cells and MUC5AC proteins decreased, and the increased levels of caspase-3 proteins and inflammatory cytokines were observed in the ocular surface tissues and lacrimal glands.

Conclusions

This CDS could create a dry environment, in which the rabbits exhibited a pathological change in dry eye similar to that in humans.

Translational Relevance

This model would be helpful in offering a platform to identify and test candidate therapies for environment-induced dry eye and to explore its underlying mechanisms.

Animal models of dry eye: Their strengths and limitations for studying human dry eye disease

Dry eye disease (DED), also called the keratoconjunctivitis sicca, is one of the most common diseases in the ophthalmology clinics. While DED is not a life-threatening disease, life quality may be substantially affected by the discomfort and the complications of poor vision. As such, a large number of studies have made contributions to the investigation of the DED pathogenesis and novel treatments. DED is a multifactorial disease featured with various phenotypic consequences; therefore, animal models are valuable tools suitable for the related studies. Accordingly, selection of the animal model to recapitulate the clinical presentation of interest is important for appropriately addressing the research objective. To this end, we systemically reviewed different murine and rabbit models of DED, which are categorized into the quantitative (aqueous-deficient) type and the qualitative (evaporative) type, based on the schemes to establish. The clinical manifestations of dry eye on animal models can be induced by mechanical or surgical approaches, iatrogenic immune response, topical eye drops, blockage of neural pathway, or others. Although these models have shown promising results, each has its own limitation and cannot fully reproduce the pathophysiological mechanisms that occur in patients. Nonetheless, the animal models remain the best approximation of human DED and represent the valuable tool for the DED studies.

Rabbit models of dry eye disease: Current understanding and unmet needs for translational research

Dry eye disease (DED) is emerging as an eye health pandemic, affecting millions worldwide. The development of novel drugs, drug delivery systems, and targeted therapies for addressing the inflammation in DED necessitates progress in experimental models of DED. Animal models of DED have been created for simulating the two clinically described forms of DED: lacrimal insufficiency and the evaporative DED models. Although most DED models have relied upon rodents, the larger eye size and longer life span of rabbits and the closer resemblance to human lacrimal glands, render rabbits a promising near-ideal model for studying DED. Since the first rabbit DED model was described, numerous modifications including the use of topical epitheliotoxic drugs, neural abolition, activated lymphocytes injection, and surgical dacryoadenectomy have been introduced. The stability of these models, whether short-term or long-term, accordingly guides their experimental or therapeutic utility. A rabbit autoimmune dacryoadenitis model has successfully simulated DED signs and features of lacrimal gland inflammation, as observed in Sjogren's syndrome, that improved with mesenchymal stem cell therapy. This review summarizes the comparative microscopic anatomy of rabbit and human lacrimal glands, various existing rabbit DED models and their respective suitability for understanding pathogenetic mechanism of DED or for experimental drug testing. Also, the insights gained from animal models in dry eye management is described along with the future perspectives. There is still a pressing need of developing rabbit models for studying the pathogenesis of complex ocular surface changes in evaporative and aqueous deficiency DED other than autoimmune dacryoadenitis.

The effect of astaxanthin on inflammation in hyperosmolarity of experimental dry eye model in vitro and in vivo

Hyperosmolarity is pro-inflammatory stress to the ocular surface epithelium associated with dry eye disease (DED). Astaxanthin (AST) is a kind of carotene, which exists in seafood and plays important roles in the amelioration of inflammatory diseases like arteriosclerosis, inflammatory bowel disease, sepsis, rheumatoid arthritis, gastric inflammation, brain inflammatory diseases. The aim of this study was to characterize the protective effect and potential mechanism of AST on DED in vitro and in vivo. Mouse models and human corneal epithelial cell (HCEC) cultures were exposed to hyperosmotic saline solution (HOSS) in in vitro and in vivo experiments, respectively. Experimental subjects were first pretreated with AST, and then the effect of the compound was assessed with clinical evaluation, real-time PCR (RT-PCR), western blot and immunofluorescent staining. We further investigated the possible mechanism of AST in DED by pre-treating with phosphoinositide 3-kinase inhibitor (LY294002). The addition of AST significantly reduced the expression of High-mobility group box 1 (HMGB1), as well as significantly inhibited the increases of TNF-α, IL-1β in a dose-dependent manner, but promoted the expression of phospho-Akt (p-Akt). BALB/c mice in DE group pretreated with AST showed significantly decreased corneal fluorescein staining scores. Moreover, pretreatment with LY294002 could eliminate the effects of AST preconditioning on the decrease of HMGB1. Our study provides evidence that AST could ameliorate DED which may be related to the inhibition of HMGB1, TNF-α, IL-1β, while PI3K/Akt signaling pathway may be involved in the expression of HMGB1 and the protective effect of AST preconditioning.

Development of New Pharmaceutical Candidates With Antioxidant Activity for the Treatment of Corneal Disorders

The ocular surface is continuously exposed to physical and chemical factors in the environment. Oxidative stress, which strongly affects the ocular surface, is caused by several factors, including ultraviolet irradiation, fine particles, and tobacco smoke. Oxidative stress is one of the pathogeneses for corneal disorders. Thus, corneal epithelium and tear fluid contain antioxidants and antioxidative enzymes to protect the cornea against oxidative stress. Because autologous serum eye drops are useful for the treatment of corneal disorders caused by dry eye, these eye drops are globally used as a therapeutic intervention in patients with dry eye. We investigated the serum components that exert antioxidative effects to clarify the mechanism of action for serum antioxidants on corneal epithelial cells and to apply these components as drugs for the treatment of corneal disorders. We found that selenoprotein P, a known selenium-transfer plasma glycoprotein, was secreted into the tear fluid to supply the corneal epithelium with selenium. Selenium participates in the regulation of oxidative stress in many tissues, including the cornea. We subsequently developed selenium compounds for application in eye drops and successfully prepared Se-COMP as a new candidate for the treatment of corneal disorders.

A New Rabbit Model of Chronic Dry Eye Disease Induced by Complete Surgical Dacryoadenectomy

Purpose/Aim: Dry eye disease (DED), common and suboptimally treated, is in need of novel animal models to understand its pathophysiology and assess the efficacy and other parameters of new pharmacological agents for its treatment. The more than 10 rabbit models of DED described to date have significant limitations including induction of mild disease, lack of consistency, and off-target effects when chemical agents are used for disease induction. Our aim was to develop a new model of chronic DED in rabbits that overcomes the limitations of existing models.

MATERIALS AND METHODS

We performed a complete surgical resection of all orbital lacrimal glands (LGs; dacryoadenectomy) in normal adult New Zealand White rabbits. One week after removal of the nictitating membrane, we surgically removed the orbital superior LG, followed by removal of the palpebral superior LG, and finally removal of the inferior LG. Surgery was performed under anesthesia, required about 1 h/eye, and was well-tolerated.

RESULTS

Dacryoadenectomy induced severe DED, evidenced by >90% reduction in the tear break up time test, 50% reduction in the Schirmer tear test, 10% increase in tear osmolarity, and a marked increase in the rose bengal staining score. DED was sustained and essentially unchanged for the eight weeks of observation. Sham-operated rabbits showed no such changes, with the exception of a non-significant and transient reduction in the tear break up time test, a response to ocular surgery.

CONCLUSIONS

This model of stable, chronic, predominantly aqueous-deficient DED recapitulates key clinical and histological features of human DED and is suitable for the study of ocular surface homeostasis, of the pathophysiology of DED, and of the efficacy of candidate drugs for DED treatment.

Multimodal Assessment of Corneal Erosions Using Optical Coherence Tomography and Automated Grading of Fluorescein Staining in a Rabbit Dry Eye Model

Purpose

To evaluate the potential use of anterior segment spectral domain optical coherence tomography (AS-SD-OCT) combined with an automated grading of fluorescein staining for assessment of corneal erosions in a rabbit short-term dry eye model.

Methods

Twenty-one New Zealand white rabbits were anesthetized and eyes were kept open for 140 minutes to induce acute corneal desiccation. Rectangular scans of the cornea were performed using Spectralis AS-SD-OCT. Total corneal thickness, corneal epithelial thickness, and the percentage of epithelial erosion area (PEEA) were evaluated. Corneas were stained with fluorescein and graded automatically using EpiView and semi-automatically using ImageJ. Spearman's rank-order correlations were calculated to compare the AS-SD-OCT PEEA and the two corneal staining scores.

Results

Eye desiccation resulted in corneal epithelium erosions that covered 0.67% to 14.2% of the central cornea (mean ± SD: 3.95% ± 3.2%) by AS-SD-OCT. The percentage of corneal area positively stained with fluorescein ranged from 0.24% to 38.01% (mean ± SD: 12.24% ± 9.7%) by using ImageJ, correlating with the AS-SD-OCT PEEA (Spearman's ρ, 0.574; P = 0.007). The EpiView score ranged from 0.5 to 10.17 and was better correlated with the AS-SD-OCT PEEA score (Spearman's ρ, 0.795; P = 0.000017).

Conclusions

Our study suggests that multimodal analysis of AS-SD-OCT and grading of fluorescein staining using EpiView software may enable quantitative assessment of corneal epithelial erosions in a rabbit short-term dry eye model.

Translational Relevance

This multimodal imaging analysis may be applied for evaluation of superficial punctate keratitis associated with dry eye.

Selenium-binding lactoferrin is taken into corneal epithelial cells by a receptor and prevents corneal damage in dry eye model animals

The ocular surface is strongly affected by oxidative stress, which causes many ocular diseases including dry eye. Previously, we showed that selenium compounds, e.g., selenoprotein P and Se-lactoferrin, were candidates for treatment of dry eye. This paper shows the efficacy of Se-lactoferrin for the treatment of dry eye compared with Diquas as a control drug using two dry eye models and incorporation of lactoferrin into corneal epithelial cells via lactoferrin receptors. We show the efficacy of Se-lactoferrin eye drops in the tobacco smoke exposure rat dry eye model and short-term rabbit dry eye model, although Diquas eye drops were only effective in the short-term rabbit dry eye model. These results indicate that Se-lactoferrin was useful in the oxidative stress-causing dry eye model. Se-lactoferrin was taken into corneal epithelium cells via lactoferrin receptors. We identified LRP1 as the lactoferrin receptor in the corneal epithelium involved in lactoferrin uptake. Se-lactoferrin eye drops did not irritate the ocular surface of rabbits. Se-lactoferrin was an excellent candidate for treatment of dry eye, reducing oxidative stress by a novel mechanism.

Age-related Defects in Ocular and Nasal Mucosal Immune System and the Immunopathology of Dry Eye Disease

Dry eye disease (DED) is a prevalent public health concern that affects up to 30% of adults and is particularly chronic and severe in the elderly. Two interconnected mechanisms cause DED: (1) an age-related dysfunction of lacrimal and meibomian glands, which leads to decreased tear production and/or an increase in tear evaporation; and (2) an age-related uncontrolled inflammation of the surface of the eye triggered by yet-to-be-determined internal immunopathological mechanisms, independent of tear deficiency and evaporation. In this review we summarize current knowledge on animal models that mimic both the severity and chronicity of inflammatory DED and that have been reliably used to provide insights into the immunopathological mechanisms of DED, and we provide an overview of the opportunities and limitations of the rabbit model in investigating the role of both ocular and nasal mucosal immune systems in the immunopathology of inflammatory DED and in testing novel immunotherapies aimed at delaying or reversing the uncontrolled age-related inflammatory DED.

Corneal-protective effects of an artificial tear containing sodium hyaluronate and castor oil on a porcine short-term dry eye model

The corneal-protective effects of an artificial tear containing sodium hyaluronate (SH) and castor oil (CO) were evaluated on a porcine short-term dry eye model. Fresh porcine eyes with an intact cornea were treated with an artificial tear of saline, SH solution (0.1%, 0.5% or 1%), CO solution (0.5%, 1% or 5%) or a mixture solution containing 0.5% SH and 1% CO and then desiccated for 60, 90 or 180 min. To assess corneal damage, the eyes were stained with methylene blue (MB) or lissamine green (LG). The staining score of MB, absorbance of MB extracted from the cornea and staining density of LG increased significantly with increasing desiccation time in untreated and all artificial tear-treated eyes, although there were no significant differences in staining scores and absorbance of MB between eyes treated continuously with saline and 1% SH-treated ones at 60 and 90 min of desiccation or the mixture-treated eyes at 60 min of desiccation. No significant differences in the staining density of LG were also found between continuous saline-treated eyes and ones desiccated for 60 min and treated with 1% SH and the mixture. Mild cytoplasmic vacuolations were histopathologically observed in the basal and wing cells in eyes desiccated for 60 min and treated with 1% SH and the mixture. The mixture solution containing 0.5% SH and 1% CO has protective effects against corneal desiccation similar to those of 1% SH and would be helpful as an artificial tear.

Corneal epithelial cell viability of an ex vivo porcine eye model

PURPOSE

The aim was to assess the consistency of corneal epithelial cell viability of an ex vivo porcine eye model.

METHOD

Six porcine eye models (four test and two control) were prepared for each experiment. The model has a computer-controlled mechanical arm, which could move the eyelid of the porcine eye and apply phosphate buffered saline to simulate blinking and lacrimation. The four test eyes were set up to simulate evaporative dry eyes with simulated lacrimation and blinking (one blink and one drop of buffered saline per minute) over three hours. Control A models were set up to collect pre-experimental baseline data, while those of control B were the same as the test eyes but without lacrimation and blinking simulation. All porcine eyes were kept in a closed chamber with temperature and humidity well controlled. After three hours, the cells of all eyes (except control A, which were assessed immediately before commencement of the experiment) were assessed. The eyes were first dipped into 0.4 per cent trypan blue solution. Following the dissection and separation of the cells, the number of dead cells were then counted under the microscope with a field size of 0.25 mm(2). The experiment was repeated 11 times.

RESULTS

No significant differences were found in the number of dead cells among the four test eyes in both the central and peripheral cornea. There were significantly more dead cells in the test eyes compared to control A but significantly less when compared to control B. More dead cells were found in the central cornea than the peripheral cornea in the test eyes but the difference was not observed in controls A and B.

CONCLUSION

Epithelial cell viabilities among the four porcine eye models with simulated lacrimation and blinking were consistent. The majority of cells were viable before the experiment and simulated lacrimation and blinking maintained more viable cells over time.

Establishment of the mild, moderate and severe dry eye models using three methods in rabbits

BACKGROUND

Dry eye (DE) is a common eye disease, and appropriate animal models are essential to explore the pathogenesis and therapy of DE. In this study, we aimed to establish rabbit models by three methods.

METHODS

In group A, the lacrimal gland, Harderian gland, and nictitating membrane of the left eyes were surgically removed. In group B, the bulbar conjunctiva of the left eyes was burned with 50% trichloroacetic acid. In group C, both methods above were used. The right eyes served as normal controls. The Schirmer I test (SIt), fluorescein staining, and impression cytology were evaluated at baseline and on days 28, 42, and 56.

RESULTS

Both the SIt and goblet cell density were significantly lower in operated eyes compared to the control eyes, while the corneal fluorescein staining scores in the operated eyes were significantly higher than in the control eyes on days 28, 42, and 56 (p < 0.05, p < 0.01 or p < 0.001). The SIt and goblet cell densities in groups B and C were significantly lower than group A on days 28, 42, and 56 (p < 0.05, p < 0.01 or p < 0.001). In addition, the corneal fluorescein staining scores in group C were significantly higher than either group A or group B on days 28, 42, and 56, while fluorescein staining scores were higher in group B than group A on days 42 and 56 days (p < 0.05, p < 0.01 or p < 0.001), with mean score 3.8 ± 1.30 (group A), 7.4 ± 1.14 (group B) and 10.8 ± 1.30 (group C) on day 56.

CONCLUSIONS

Results suggest that three separate DE models, with mild, moderate, and severe manifestations of DE, could be stably established, in which conjunctival goblet cells took an important role.

Research on the stability of a rabbit dry eye model induced by topical application of the preservative benzalkonium chloride

Background

Dry eye is a common disease worldwide, and animal models are critical for the study of it. At present, there is no research about the stability of the extant animal models, which may have negative implications for previous dry eye studies. In this study, we observed the stability of a rabbit dry eye model induced by the topical benzalkonium chloride (BAC) and determined the valid time of this model.

Methods and Findings

Eighty white rabbits were randomly divided into four groups. One eye from each rabbit was randomly chosen to receive topical 0.1% BAC twice daily for 2 weeks (Group BAC-W2), 3 weeks (Group BAC-W3), 4 weeks (Group BAC-W4), or 5 weeks (Group BAC-W5). Fluorescein staining, Schirmer's tests, and conjunctival impression cytology were performed before BAC treatment (normal) and on days 0, 7, 14 and 21 after BAC removal. The eyeballs were collected at these time points for immunofluorescence staining, hematoxylin and eosin (HE) staining, and electron microscopy. After removing BAC, the signs of dry eye in Group BAC-W2 lasted one week. Compared with normal, there were still significant differences in the results of Schirmer's tests and fluorescein staining in Groups BAC-W3 and BAC-W4 on day 7 (P<0.05) and in Group BAC-W5 on day 14 (P<0.05). Decreases in goblet cell density remained stable in the three experimental groups at all time points (P<0.001). Decreased levels of mucin-5 subtype AC (MUC5AC), along with histopathological and ultrastructural disorders of the cornea and conjunctiva could be observed in Group BAC-W4 and particularly in Group BAC-W5 until day 21.

Conclusions

A stable rabbit dry eye model was induced by topical 0.1% BAC for 5 weeks, and after BAC removal, the signs of dry eye were sustained for 2 weeks (for the mixed type of dry eye) or for at least 3 weeks (for mucin-deficient dry eye).

A new experimental device to evaluate eye ulcers using a multispectral electrical impedance technique

We present a novel experimental technique to determine eye ulcers in animals using a spectral electrical impedance technique. We expect that this technique will be useful in dry eye syndrome. We used a sensor that is basically a platinum (Pt) microelectrode electrically insulated by glass from a cylindrical stainless steel counter-electrode. This sensor was applied to the naked eye of New Zealand rabbits (2.0-3.5 kg in weight). Whereas half of the eyes were normal (control), we applied to the remainder a few drops of 20% (v/v) alcohol to produce an ulcer in the eye. Using a multispectral electrical impedance system we measured ulcerated and control eyes and observed significant difference between normal and pathological samples. We also investigated the effects of different applied pressures and natural degradation of initially normal eyes as a function of time. We believe that this technique could be sufficiently sensitive and repetitive to help diagnose ocular surface diseases such as dry eye syndrome.

Acute ocular injuries caused by 60-Ghz millimeter-wave exposure

The goal of this study was to examine the clinical course of 60-GHz millimeter-wave induced damages to the rabbit eye and to report experimental conditions that allow reproducible induction of these injuries. The eyes of pigmented rabbits (total number was 40) were irradiated with 60-GHz millimeter-waves using either a horn antenna or one of two lens antennas (6 and 9 mm diameter; phi6, phi9) Morphological changes were assessed by slit-lamp microscopy. Additional assessments included corneal fluorescein staining, iris fluorescein angiography, and lens epithelium light microscopy. Under the standardized eye-antenna positioning, the three antennas caused varying damages to the eyelids or eyeglobes. The most reproducible injuries without concurrent eyelid edema and corneal desiccation were achieved using the phi6 lens antenna: irradiation for 6 min led to an elevation of the corneal surface temperature (reaching 54.2 +/- 0.9 degrees C) plus corneal edema and epithelial cell loss. Furthermore, mitotic cells appeared in the pupillary area of the lens epithelium. Anterior uveitis also occurred resulting in acute miosis (from 6.6 +/- 1.4 to 2.2 +/- 1.4 mm), an increase in flares (from 6.7 +/- 0.9 to 334.3 +/- 130.8 photons per second), and iris vasodilation or vessel leakage. These findings indicate that the three types of millimeter-wave antennas can cause thermal injuries of varying types and levels. The thermal effects induced by millimeter-waves can apparently penetrate below the surface of the eye.

A novel porcine dry eye model system (pDEM) with simulated lacrimation/blinking system: Preliminary findings on system variability and effect of corneal drying

PURPOSE

To investigate inter- and intra-system variations and the effect of corneal drying using a recently developed pDEM.

METHODS

pDEM was used to simulate "normal" and "dry eye" conditions using two "lacrimation-blink" intervals (20 s and 60 s). Corneas were examined/graded with sodium fluorescein before and after the experiment. At the end of each experiment, corneas were assessed by trypan blue exclusion technique. Two duplicated pDEM systems were set up and tested to investigate reproducibility.

RESULTS

There was no significant difference in the results produced by the two pDEM systems. In the eyes under "normal" condition, there was no significant increase in the fluorescein grading. However, in eyes under "dry eye" condition, fluorescein staining increased and the number of non-viable cells in the central cornea increased.

CONCLUSIONS

This novel pDEM system provides a useful assessment tool for the study of causative factors and new treatment strategies for dry eye syndrome.

Evaluation of novel dry eye model: preganglionic parasympathetic denervation in rabbit

PURPOSE

To evaluate ocular surface status after interruption of preganglionic, parasympathetic neural control after surgical removal of the greater superficial petrosal nerve (GSPN).

METHODS

New Zealand White rabbits underwent unilateral section and removal of a 5-mm portion of the GSPN by a route through the inner ear; no ocular or orbital tissue was involved. Before and 7 days after surgery, all animals underwent preliminary examination, including fluorescein staining, rose bengal instillation, blink rate, tear breakup time (BUT), tear flow, and impression cytology. Total tarsorrhaphy was carried out in four additional rabbits, and another four animals underwent unilateral sham procedures. The GSPN, pterygopalatine ganglion, lacrimal gland, and conjunctiva were evaluated by light and transmission electron microscopy (TEM).

RESULTS

GSPN sectioning resulted in significant changes of the ocular surface after 7 days: intense rose bengal staining of the conjunctiva, fluorescein staining of the cornea, increased blink rate (P < 0.05), decreased BUT (P < 0.005), decreased tear flow by 26% (P < 0.005), and decreased goblet cell density (P < 0.01). TEM revealed massive accumulation of secretory granules in lacrimal acinar cells. The changes were also seen after tarsorrhaphy. Neither the contralateral control nor the sham eyes were affected.

CONCLUSIONS

The effects of GSPN nerve section led to the rapid onset of a dry eye condition in the rabbits that continued for at least 1 week. The authors suggest that continuous neural drive of the pterygopalatine ganglion is necessary to maintain adequate tear flow and mucin secretion. It is likely the trigeminal system is the afferent origin of this continuous neural tone.

Comparison of topical dry eye medications for the treatment of keratoconjunctivitis sicca in a botulinum toxin B-induced mouse model

PURPOSE

To compare the effects of topical dry eye medications including anti-inflammatory agents and lubricant eyedrops for the treatment of keratoconjunctivitis sicca (KCS) in a botulinum toxin B (BTX-B)-induced mouse model.

METHODS

CBA mice were randomized into 10 groups. The first 5 groups received a transconjunctival injection of saline into the lacrimal gland, and the remaining groups were injected with 0.05 mL of 20 mU BTX-B. Each group received treatment with 0.1% fluorometholone (FML), 0.05% cyclosporine A (CsA), a 50:50 combination of FML and CsA, artificial tears, or saline 3 days after injections. Tear production, corneal staining, and blink rate were compared in each of the 10 groups.

RESULTS

Tear production in BTX-B-injected CsA-treated, FML-treated, and combined-treated groups started to return to baseline level within 2 weeks of treatment, whereas those treated with saline or artificial tears still exhibited reduction of lacrimation up to 4 weeks after injection. Topical FML significantly reversed the staining score within 1 week of treatment. The improvement of corneal staining in BTX-B-challenged combined-treated and CsA-treated groups occurred later within 2 weeks after treatment. No significant improvement in corneal staining was observed for the BTX-B-injected mice treated with artificial tears or saline. No significant changes were noted in blink frequency between the control and study groups undergoing the various dry eye therapies.

CONCLUSION

The therapeutic effects of dry eye medications in a BTX-B-induced mouse model of KCS are similar to the human response.

Investigation of Corneal Effect of Different Types of Artificial Tears in a Simulated Dry Eye Condition Using a Novel Porcine Dry Eye Model (pDEM)

PURPOSE

To use a novel porcine dry eye model (pDEM) to study the effect of various artificial tears on corneal abrasion and epithelial cell death under severe "dry eye" conditions.

METHODS

A 60-second lacrimation-blink interval, which simulates a severe dry eye condition, was set up with our novel pDEM. The corneal protective effect of lubricating the eye for 4 hours with Dulbecco phosphate-buffered saline (DPBS, as control; n = 20) and with 3 types of commercially available artificial tears (n = 17 for each) that contained different lubricating agents was studied. Effect was determined in terms of the change in fluorescein staining grade (on a 0-4 point scale with 0.5 increments) of the cornea and the number of dead cells (by trypan blue staining) on the corneal surface.

RESULTS

Median increase in fluorescein grading (median) in corneas treated for 4 hours with artificial tears containing sodium hyaluronate or hydroxypropyl methylcellulose was significantly (P < 0.002) smaller than with artificial tears containing balanced saline with an unknown demulcent or the DPBS control. The numbers of dead epithelial cells in the central corneas lubricated with artificial tears containing sodium hyaluronate or hydroxypropyl methylcellulose (229 +/- 71 and 221 +/- 65 [SD], respectively) were also significantly (P < 0.005) smaller than those in the corneas of eyes lubricated with artificial tears containing balanced saline with an unknown demulcent or DPBS alone (328 +/- 106 and 341 +/- 113, respectively).

CONCLUSION

Results show that artificial tears containing sodium hyaluronate or hydroxypropyl methylcellulose as lubricating agents give enhanced corneal protection against desiccation and show the use of this novel pDEM model in evaluating corneal protection from desiccation.

Effects of various lubricants on corneal surface regularity in rabbits

The aim of this study was to establish a method for analysis of tear film stability and thereby to investigate the effects of lubricants on corneal surface regularity and corneal epithelial damage in anesthetized rabbits with the eye held open. Saline-instilled and noninstilled eyes manifested a time-dependent increase in the corneal surface regularity index (SRI). In contrast, 0.1% hyaluronic acid (HA) prevented the increase in the SRI for up to 20 min after instillation. Methylene blue uptake into the damaged cornea was significantly greater in eyes that received saline than in those treated with HA. Whereas eyes instilled with 0.5% methylcellulose (MC) or 0.35% sodium carboxymethylcellulose (CMC) manifested an increase in the SRI similar to that apparent in those that received saline, 1.0% chondroitin sulfate (CS) prevented the increase in the SRI for up to 10 min after instillation. In conclusion, we have established a method for analysis of tear film stability in rabbits. Our results suggest that tear film stability is closely related to corneal surface damage and that topical instillation of 0.1% HA or 1.0% chondroitin sulfate warrants further investigation as a potential treatment for patients with dry eye.

A convenient rabbit model of ocular epithelium damage induced by osmotic dehydration

Dry eye is an ocular disease clinically associated with corneal epithelium damage and arises acutely or chronically from dehydration of the ocular surface. We provide herein a novel in vivo model of corneal epithelium damage, in which the corneal surface was entirely covered with a sugar powder to provoke the rapid removal of corneal surface liquid. In this animal model, such corneal damage as can be fluorometrically detected was observed immediately after 20-minute hyperosmotic treatment, reached a maximum 6 hours later, and then gradually declined to complete recovery at Hour 126. Recovery of the damaged corneas produced by hyperosmotic stress was significantly accelerated by treatment with 0.1% sodium hyaluronate, a dry eye remedy in Japan. Thinning or partial erosion of the epithelial cell layers was histopathologically demonstrated in and around the sugar powder-applied area but the posterior stromal cell layer remained intact, indicating that the present rabbit in vivo model may be used to conveniently screen therapeutics against acute ocular diseases with corneal epithelium damage. In addition, microscopic observations of TUNEL-stained thin-sections of the damaged corneas indicated that apoptotic cell death, but not any inflammatory reactions, may be at least partially responsible for the hyperosmolarity-induced destruction of the corneal epithelium.

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.

Lactoferrin suppresses loss of corneal epithelial integrity in a rabbit short-term dry eye model

Human tear fluid contains lactoferrin at the highest concentration. In patients with dry eye such as Sjogren's syndrome, the concentration of lactoferrin in the tears is approximately half the normal value. The present study utilizes a short-term rabbit dry eye model to evaluate if lactoferrin containing eye drops can reverse any of the damage produced by blockage of blinking with an ocular speculum. Damage was evaluated based on the extent of methylene blue staining in histological sections. After 3 h of desiccation, the amount of extractable dye recovered following sacrifice increased by more than 4-fold in the vehicle-treated eyes. However, in those rabbits treated with 1% lactoferrin, dye recovery was only 40% of the value in the vehicle-treated eyes. Between 1-3 h and over a concentration range from 0.01 to 1% lactoferrin, the decreases in staining were both time and concentration dependent. Alternatively, if 1% lactoferrin was applied during the desiccation period, there was partial restoration of corneal epithelial integrity. These results suggest that lactoferrin may be of therapeutic value in decreasing the loss of corneal epithelial integrity in dry eye.

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

The effect of drugs for gastritis and gastric ulcer (ecabet sodium, gefarnate, teprenone, and troxipide) on the secretion of mucin-like glycoproteins from rat cornea were investigated in vitro and on a short-term, rabbit dry eye model in vivo. For the studies in vitro, cultured rat cornea sections (3 mm diameter) were incubated with radiolabeled sodium sulfate, rinsed, and then incubated for 30 min in the presence of one of the drugs. The culture media were reacted with Dolichos biflorus agglutinate (DBA)-lectin, and the radioactivity of DBA-bound mucin-like glycoproteins was measured. A cytotoxicity assay confirmed that mucin-like glycoproteins had not leaked from damaged cells. For studies in vivo, eye drop vehicle or drops containing gefarnate were instilled in the eyes of nine anesthetized rabbits, and then the eyes were kept open with specula for two hours. These rabbits and two control rabbits not subjected to ocular drying were killed, and their eyes were enucleated and stained with methylene blue. Corneal epithelial damage from desiccation was evaluated based on the extent of methylene blue staining. Among the four kinds of drugs for gastritis and gastric ulcers, only gefarnate significantly increased the mucin-like glycoprotein secretion from cultured rat corneas in vitro; this stimulatory effect of gefarnate was dose-dependent. In vivo, the instillation of gefarnate reduced corneal epithelial damage from desiccation in a dose-dependent fashion. These results suggest that gefarnate reduces desiccation of corneal epithelium, perhaps by stimulating secretion of mucin-like glycoproteins from corneal epithelium.