Rabbit as an Animal Model for Ocular Surface Disease, Tear Osmolarity, Electrolyte, and Tear Ferning Profiles

Coenzyme Q10 microemulsion ion-activated gel: a promising ophthalmic delivery system for enhanced corneal protection and sustained release

PURPOSE

This study aimed to evaluate a novel microemulsion ion-activated gel system for the ophthalmic delivery of coenzyme Q10 (CoQ10).

METHODS

Various CoQ10 microemulsion ion-activated formulations were prepared and fully assessed for physical and chemical parameters, assay and related substances, in vitro release, rheological properties, in vitro cytotoxicity and ophthalmic retention. A preliminary pharmacokinetic study was also performed in rabbits.

RESULTS

The formulations met the specified criteria, showing a droplet size of 24.5 ± 2.0 nm for microemulsions, increasing slightly to 39.6 ± 3.5 nm for the microemulsion gels. They exhibited a 24-hour sustained in vitro release (80.0% ± 3.2%) and increased viscosity upon contact with artificial tears containing Ca2+ and K+ ions. The no-film dissolution method and in vitro models indicated first-order release kinetics (r = 0.987). The preparations demonstrated good tolerance and non-irritating properties, with a Draize score of 0-0.55 in rabbits, and provided a 2-hour extension in drug retention on the ocular surface compared with microemulsions alone. In ultraviolet B (UVB)-exposed rats, corneal epithelial damage was reduced and antioxidant marker levels (superoxide dismutase, malondialdehyde) were significantly improved.

CONCLUSION

This novel system is a promising preparation for ophthalmic CoQ10 delivery, offering sustained release and protection against UVB-induced corneal damage.

Characterizing the Robustness of Distinct Clinical Assessments in Identifying Dry Eye Condition of Animal Models

PURPOSE

The study aims to characterize the robustness of distinct clinical assessments in identifying the underlying conditions of dry eye disease (DED), with a specific emphasis on the involvement of conjunctival goblet cells.

METHODS

Seven rabbits receiving surgical removal of the lacrimal and Harderian glands were divided into two groups, one with ablation of conjunctival goblet cells by topical soaking of trichloroacetic acid (TCA) to the bulbar conjunctiva (n = 3) and one without (n = 4), and the conditions of DED were assessed weekly using Schirmer test, tear breakup time (TBUT), tear osmolarity, and National Eye Institute (NEI) fluorescein staining grading. After 8 weeks, the rabbits were sacrificed, and the eyes were enucleated for histopathological examination.

RESULTS

Histopathological analysis revealed corneal epithelial thinning in both groups. While TCA soaking significantly decreased the density of conjunctival goblet cells, DED rabbits without TCA also showed a partial reduction in goblet cell density, potentially attributable to dacryoadenectomy. Both groups showed significant decreases in Schirmer test and TBUT, as well as an increase in tear osmolarity. In DED rabbits with TCA soaking, tear osmolarity increased markedly, suggesting that tear osmolarity is highly sensitive to loss and/or dysfunction of conjunctival goblet cells. Fluorescein staining was gradually and similarly increased in both groups, suggesting that fluorescein staining may not reveal an early disruption of the tear film until the prolonged progression of DED.

CONCLUSION

The Schirmer test, TBUT, tear osmolarity, and NEI fluorescein grading are distinct, yet complementary, clinical assessments for the evaluation of DED. By performing these assessments in definitive DED rabbit models, both with and without ablation of conjunctival goblet cells, the role of these cells in the homeostasis of tear osmolarity is highlighted. Characterizing the robustness of these assessments in identifying the underlying conditions of DED will guide a more appropriate management for patients with DED.

Topical Solution for Retinal Delivery: Bevacizumab and Ranibizumab Eye Drops in Anti-Aggregation Formula (AAF) in Rabbits

PURPOSE

Wet age-related macular degeneration (AMD) is a blinding retinal disease. Monthly intravitreal anti-VEGF antibody injections of bevacizumab (off-label) and ranibizumab (FDA approved) are the standard of care. Antibody aggregation may interfere with ocular absorption/distribution. This study assessed topical delivery of dilute antibodies to the posterior segment of rabbit eyes using a novel anti-aggregation formula (AAF).

METHODS

Bevacizumab, or biosimilar ranibizumab was diluted to 5 mg/ml in AAF. All rabbits were dosed twice daily. Substudy 1 rabbits (bevacizumab, 100 µl eye drops): Group 1 (bevacizumab/AAF, n = 6); Group 2 (bevacizumab/PBS, n = 7) and Vehicle control (AAF, n = 1). Substudy 2 rabbits (ranibizumab biosimilar/AAF, 50 µl eye drops): (ranibizumab biosimilar/AAF, n = 8). At 14.5 days, serum was drawn from rabbits. Aqueous, vitreous and retina samples were recovered from eyes and placed into AAF aliquots. Tissue analyzed using AAF as diluent.

RESULTS

Bevacizumab in AAF permeated/accumulated in rabbit aqueous, vitreous and retina 10 times more, than when diluted in PBS. AAF/0.1% hyaluronic acid eye drops, dosed twice daily, provided mean tissue concentrations (ng/g) in retina (29.50), aqueous (12.34), vitreous (3.46), and serum (0.28 ng/ml). Additionally, the highest concentration (ng/g) of ranibizumab biosimilar was present in the retina (18.0), followed by aqueous (7.82) and vitreous (1.47). Serum concentration was negligible (< 0.04 ng/ml). No irritation was observed throughout the studies.

CONCLUSIONS

Bevacizumab and ranibizumab, in an AAF diluent eye drop, can be delivered to the retina, by the twice daily dosing of a low concentration mAb formulation. This may prove to be an adjunct to intravitreal injections.

Clinical parameters obtained during tear film examination in domestic rabbits

Background

One of the contributing factors to ocular surface health is a stable precorneal tear film. Considering the increasing interest in rabbits as pets and the limited literature available on domestic rabbit tearing, the aim of this study was to establish normative data for examination of the tear film in domestic rabbits.

Results

The study included 75 client-owned domestic Holland Lop rabbits (150 eyes). The following examinations were performed in each eye: Schirmer tear test-1, tear osmometry, interferometry, tear meniscus height measurement and meibography (quantifying meibomian gland loss as a percentage). The resulting median (95% central range) values were 10.0 (5.0–17.3) mm/min for the Schirmer tear test-1, 345.0 (280.5–376.1) mOsm/L for tear osmolarity, grade 2 (1–4) of interferometry, 0.28 (0.20–0.47) mm for tear meniscus height and 0.0 (0.0–67.6) % meibomian gland loss. A significant association was found between tear osmolarity and age, with an estimated decrease of − 4.0 mOsm/L with each additional year of age (p < 0.001). The distributions of interferometry grades were significantly different between males and females (p < 0.001), with grade 1 and grade 2 being the most frequent in females and males, respectively. A weak negative correlation was also observed between interferometry grade and the percentage of meibomian gland loss (r = − 0.22, p = 0.006).

Conclusions

This is an original study that documents extensive tear film parameters in healthy Holland Lop rabbits. The results can be used as normative data for the examination of the tear film in this lagomorph breed.

Benzalkonium Chloride for Experimental Dry Eye Induction in a Rabbit Model

Purpose: This study compared the clinical parameters and histological findings according to the benzalkonium chloride concentration (BAC; 0.05%, 0.1%, and 0.2%) for inducing experimental dry eye (EDE) in a rabbit model.Methods: Rabbits were divided into four groups according to the BAC concentration: untreated group, 0.05%, 0.1%, and 0.2% BAC. BAC was instilled topically in both eyes of the rabbits twice daily until they were euthanized after 14 days. Tear volume, tear break-up time (TBUT), and corneal fluorescein staining score (CFS) were measured 0, 3, 5, 7, and 14 days after treatment. After excising tissues on day 14, the conjunctival goblet cell density and corneal epithelial apoptosis were quantified.Results: The tear volume and TBUT were lower and the CFS was higher than baseline values after 14, 10, and 5 days in the 0.05, 0.1, and 0.2% BAC groups, respectively (all p < 0.05). At 14 days, the 0.2% BAC group showed more significant aggravation of all clinical parameters, and the 0.1% BAC group had a lower CFS (all p < 0.05) than the 0.05% BAC group. In all BAC groups, the conjunctival goblet cell density was lower and corneal epithelial apoptosis was significantly higher than in the untreated group (all p < 0.01). The conjunctival goblet cell density was lower in the 0.2% BAC group than in the 0.05% BAC group. Between-group differences in corneal epithelial apoptosis were observed in all experimental groups (all p < 0.01).Conclusions: Instilling BAC for 14 days induced EDE in the 0.05, 0.1, and 0.2% BAC groups. Although 0.2% BAC cannot be used for a severe EDE model, it is useful for inducing EDE in a rabbit model in a short time.

Modeling the antioxidant properties of the eye reduces the false-positive rate of a nonanimal eye irritation test (OptiSafe)

We recently identified a group of chemicals that are misclassified by most, if not all, in vitro alternative ocular irritation tests, suggesting that nonanimal tests may not fully model the ocular environment in which these chemicals interact. To address this, we evaluated the composition of tears, the first defense against foreign substances, and identified the presence of antioxidants that could detoxify reactive chemicals that otherwise may be falsely identified as irritants in alternative irritation tests. In this study, we evaluated the effects of tear antioxidants on the ocular irritation scoring of commonly overclassified chemicals (false positives) using the OptiSafe™ ocular irritation test. Six tear-related antioxidants were individually added to the OptiSafe formulation, and the effects on test outcome were determined. Ascorbic acid, the most abundant water-soluble antioxidant in tears, specifically reduced the OptiSafe false-positive rate. Titration curves showed that this reduction occurs at in vivo concentrations and is specific to chemicals identified either as producing reactive oxygen species or as crosslinkers. Importantly, the addition of tear antioxidants did not impact the detection of true negatives, true positives, or other false positives unassociated with reactive oxygen species or crosslinking. These results suggest that the addition of tear antioxidants to in vitro alternative test systems may substantially reduce the false-positive rate and improve ocular irritant detection.