Safety and Tolerability of Overdosed Artificial Tears by Abraded Rabbit Corneas

Impact of Latanoprost Antiglaucoma Eyedrops and Their Excipients on Toxicity and Healing Characteristics in the Ex Vivo Eye Irritation Test System

INTRODUCTION

Corneal epithelial toxicity and delayed healing process have already been attributed to preservatives or some excipients. We study the effects of galenic components in antiglaucoma drugs such as benzalkonium chloride (BAC) or surfactants like macrogolglycerol hydroxystearate 40 (MGHS 40) on corneal toxicity in an ex vivo system mimicking chronic use.

METHODS

Latanoprost-containing eyedrops are available with and without preservatives on the market. Unpreserved, they are available in different formulations with various excipients like MGHS at different concentrations (0%, 2.5%, and 5%). We studied these in the ex vivo bioreactor (EVEIT) on initially injured rabbit corneas. The drugs were applied six times daily for observation periods of 3 or 5 days. BAC, 5% MGHS 40 solution, and 0.18% hyaluronic acid served as controls. Macroscopic photographic, biochemical methods and corneal integrity quantification were used for evaluation. Toxicity was assessed by measuring wound healing and corneal fluorescein sodium permeability and was confirmed by histology studies.

RESULTS

The BAC-preserved formulation resulted in high corneal toxicity, which was expected. Interestingly, the preservative-free (PF) formulation containing 5% MGHS 40, carbomer, macrogol 4000, and sorbitol showed the highest corneal toxicity, followed by the control formulation with equal MGHS 40 concentration, which presented significantly less damage. No toxicity was shown by eyedrops containing 2.5% MGHS 40 or salts only.

CONCLUSION

Our study demonstrates a significant corneal toxicity of certain formulations of PF antiglaucoma ophthalmic drugs containing 5% MGHS 40 with other excipients compared to other formulations with lower MGHS 40 concentrations (2.5% or 0%), or even compared to the solution containing 5% MGHS alone. This suggests a concentration-dependent toxicity of MGHS 40, especially in interaction with other excipients, which may increase its epithelial toxicity, and that has to be considered in clinical glaucoma therapy. Further single-component formulation trials are needed to support this interpretation.

Characteristics of histamine H4 receptor agonist-induced allergic conjunctivitis model in Guinea pigs

Histamine is strongly associated with the onset of allergic conjunctivitis. The most recent cloned histamine H₄ receptor antagonist is highly expected as a new therapeutic drug candidate. As a model for a therapeutic drug targeting the histamine H₄ receptor, a mouse model in which conjunctivitis symptoms are induced by instilling 4-methylhistamine, a histamine H₄ receptor agonist, has been reported. However, the affinity of the H₄ receptor for histamine varies in species, and it is known that the histamine binding affinity for the guinea pig H₄ receptor is closer to that for human receptor than mice receptor. In this paper, we investigated a possibility that a guinea pig model would become a drug efficacy evaluation model with higher evaluation accuracy than the mouse model. As a result, hyperemia was observed in the conjunctivae and iris of guinea pigs after instillation of 4-methylhistamine and specifically suppressed by the histamine H₄ receptor antagonist. Unlikely to the previously reported mouse model, however, none of edema, increased vascular permeability or scratching behavior was observed, suggesting that there may be differences between mice and guinea pigs not only in the binding affinity of histamine to the H₄ receptor but also in the biological reaction to 4-methylhistamine. Although the symptoms of allergic conjunctivitis do not appear comprehensively in the guinea pig model, results of this study indicated a possibility that this model can be used as a simple screening model in the early stages of drug development.

A novel ophthalmic latanoprost 0.005% nanoemulsion: a cytotoxicity study

BACKGROUND

Benzalkonium chloride (BAK), the most commonly used preservative in anti-glaucoma eye drops, inflicts damage to the ocular surface. A novel anti-glaucoma formulation that avoids the use of BAK has been developed. The aim of this study was to evaluate the cytotoxicity of this formulation and to compare it with an ophthalmic solution containing BAK.

METHODS

Two different latanoprost eye drops were used: one ophthalmic solution (LSc) containing BAK 0.02% and one ophthalmic nanoemulsion (LNe) with a soft preservative (potassium sorbate 0.18%). Human epithelial conjunctival cells were incubated for 15, 30, and 60 min with either LSc or LNe. The cytotoxicity was determined by MTT assay. Cell death was measured by flow cytometry using annexin V-FITC and propidium iodide.

RESULTS

The values of cell viability and proliferation obtained from cells exposed to LNe were between 80 and 90% relative to the control group, whereas values obtained from cells exposed to LSc were around 30% at all study times (p < 0.05 at 15 and 30 min; p < 0.01 at 60 min). The percentage of viable cells decreased significantly when cells were incubated with LSc compared with cells incubated with LNe at all the study times, while the percentage of cells in late apoptosis/necrosis increased significantly in cells exposed to LSc compared to LNe.

CONCLUSIONS

The new latanoprost nanoemulsion is significantly less cytotoxic on human conjunctival cells than LSc. These results suggest that the new formulation might be gentler on the eye surface than currently available BAK-preserved latanoprost solutions.

Dynamics of a Gel-Based Artificial Tear Film with an Emphasis on Dry Disease Treatment Applications

This paper discusses the spreading of gel-based ophthalmic formulation on the cornea surface assumed to be flat. We show that gel-based formulations exhibit rheological behaviors that the Herschel–Bulkley model can describe. The continuity and momentum equations are solved numerically using the monofluid formulation and the volume-of-fluid (VOF) method. We investigated the influence of the rheological properties, namely the consistency, the yield stress, and the flow behavior index, on the spreading of a gel-based artificial tear over the cornea surface. We propose optimal values of these properties for efficient gel-based artificial tears.

Short-term effect of non-preserved cationic oil-in-water ophthalmic emulsion on tear meniscus parameters of healthy individuals in a prospective, controlled pilot study

Background

This study investigated the effect of instilling a single drop of non-preserved cationic oil-in- water ophthalmic emulsion (Cationorm®) on the lower (LTM) and upper tear meniscus (UTM) parameters of normal eyes.

Methods

In this prospective, single-center, non-randomized, controlled pilot study, optical coherence tomography was used to estimate the UTM and LTM height, depth, and cross-sectional area in participants without a history of dry eye disease. In the right eye (study eye), we instilled one drop of Cationorm® in the lower conjunctival sac. Scans of the tear menisci were acquired at baseline, before the instillation, and at 5, 15, and 30 min thereafter. Control scans of the left eye (control eye) were obtained at the same timepoints. The tear meniscus parameters of the study eye were compared with the control eye at each timepoint.

Results

Twenty subjects (11 male and 9 female; mean [standard deviation] of age: 37.8 [10.9] years) were included in the study. Compared to the control eye, instillation of a single drop of Cationorm® resulted in significantly higher LTM parameter values and a higher UTM cross-sectional area up to 30 min after instillation (all P < 0.05). The UTM height and depth were significantly greater in the study eye than in the control eye up to 5 min (P < 0.001 and 0.007, respectively) and 15-min (P = 0.045, and 0.002, respectively) after Cationorm® instillation. In the study eye, Cationorm® resulted in a significant increase in LTM parameter values up to 30 min post-instillation (all P < 0.001). The UTM height was significantly greater up to 15 min post-instillation than at baseline. The UTM depth and area increased significantly from baseline to 5 min after instillation (P = 0.043, and 0.002, respectively).

Conclusions

Cationorm® seems to have a prolonged residence time on the ocular surface of healthy subjects as indicated by LTM parameters and to a lesser extent by UTM parameters.

High-Frequency Application of Cationic Agents Containing Lubricant Eye Drops Causes Cumulative Corneal Toxicity in an Ex Vivo Eye Irritation Test Model

Purpose: High-frequency applied cetalkonium chloride (CAC) and benzalkonium chloride (BAC) 0.02% did not hamper corneal healing in a living rabbit model of induced corneal erosion. In contrast, the ex vivo eye irritation test (EVEIT) shows inhibition of healing for these substances. In a systematic ex vivo reproduction of the in vivo experiments, we discuss the background of these differences. Methods: Excised rabbit corneas (n = 5 per group) were cultured in artificial anterior chambers (EVEIT). Four erosions were induced for each cornea before starting regular 21 installations/day over 3 days of (1) CAC containing eye drops (Cationorm^®), (2) 0.02% BAC. Corneal fluorescein staining, quantification of glucose-/lactate consumption, and histology were performed. Results: BAC 0.02% treated corneas showed increased epithelial lesions from 10.13 ± 0.65 mm² to 10 ± 0.8 mm² on day 0, to 86.82 ± 5.18 mm² (P < 0.0001) by day 3. After a trend toward smaller lesions for CAC on day 1, erosion sizes increased significantly by day 3 from 9.82 ± 0.30 mm² to 29.51 ± 16.87 mm² (P < 0.05). For 1 cornea, corneal erosions nearly disappeared on day 3 (0.89 mm²). Corneal lactate increased significantly for BAC and CAC, whereas glucose concentrations were unchanged. Histology revealed disintegration of the corneal structures for both compounds. Conclusions: The data underline the EVEIT as a predictive toxicity test to show side effects in a time-compressed manner. The consistency of these predictions was previously demonstrated by the EVEIT for BAC, phosphate buffer, and others. The EVEIT is suited for a chronic application prediction of tolerability and toxic side effects of eye drops in particular, and other chemicals in general.

Cationic Emulsion-Based Artificial Tears as a Mimic of Functional Healthy Tear Film for Restoration of Ocular Surface Homeostasis in Dry Eye Disease

Dry eye disease (DED) is a complex multifactorial disease that affects an increasing number of patients worldwide. Close to 30% of the population has experienced dry eye (DE) symptoms and presented with some signs of the disease during their lifetime. The significant heterogeneity in the medical background of patients with DEs and in their sensitivity to symptoms renders a clear understanding of DED complicated. It has become evident over the past few years that DED results from an impairment of the ocular surface homeostasis. Hence, a holistic treatment approach that concomitantly addresses the different mechanisms that result in the destabilization of the tear film (TF) and the ocular surface would be appropriate. The goal of the present review is to compile the different types of scientific evidence (from in silico modeling to clinical trials) that help explain the mechanism of action of cationic emulsion (CE)-based eye drop technology for the treatment of both the signs and the symptoms of DED. These CE-based artificial tear (AT) eye drops designed to mimic, from a functional point of view, a healthy TF contribute to the restoration of a healthy ocular surface environment and TF that leads to a better management of DE patients. The CE-based AT eye drops help restore the ocular surface homeostasis in patients who have unstable TF or no tears.

Corneal Injury Detection Using Apple iOS-Based Application Technology

PURPOSE

To describe the feasibility of an attachment-free iOS-based cobalt blue light application to accurately detect corneal injury.

METHODS

Corneal epithelium from New Zealand White rabbits was removed by gentle scraping with a dulled scalpel or by using a classic biopsy punch (2 mm in diameter). Each cornea was then examined using a smartphone-enabled blue light after applying a fluorescein sodium ophthalmic strip. Photographs of each cornea before and after using the smartphone-based light were captured with a second smartphone device.

RESULTS

The iOS-based (Apple Inc., Cuptertino, CA) cobalt blue light effectively illuminated fluorescein dye in all ex vivo samples. Both circular punch biopsy and linear scalpel-induced corneal injuries were readily identified.

CONCLUSIONS

The iOS-based cobalt blue light is a portable, low-cost, and effective alternative to commercially available cobalt blue lights.