Development of In Vitro Methodologies to Investigate Binding by Sodium Hyaluronate in Eye Drops to Corneal Surfaces.

Udo Bock,Jochner M,Von Deylen D,Stäbler C,Doerr M,Reichl S

doi:10.2174/1874364101812010226

Abstract

Purpose:To develop in vitro methods to assess binding by sodium hyaluronate in eye drops to corneal surfaces.Methods:Two different, complementary corneal binding set-ups were developed. In a dynamic in vitro model, confluent corneal epithelial cells (HCE-T) were assembled in chamber slides and a declining channel. A static model was constructed with ex vivo porcine corneas clamped in Franz cells. To test the predictive capacity of models, four different eye drops containing sodium hyaluronate were spiked with tritium-labeled sodium hyaluronate to standardize quantification. In both settings, eye drops were applied for 5 min and physiological conditions were mimicked by flushing with artificial tear fluid. Spreading experiments on HCE-T next to synthetic membranes were used for further characterization.Results:Binding was more pronounced in dynamic HCE-T model. Three of the four eye drops demonstrated sigmoidal elution of sodium hyaluronate, suggesting pronounced binding. One solution eluted distinctly faster, likewise the buffer control. The static method produced a similar ranking but at lower levels. When eye drops in which phosphate buffer was replaced by citrate buffer (i.e., to prevent calcification) were used, binding was not influenced. All eye drops spread immediately when placed on HCE-T and at the same order of magnitude on glass and polyethylene terephthalate surfaces.Conclusion:Dynamic and static models performed on different corneal sources were used to determine sodium hyaluronate binding kinetics in solutions under physiological conditions. These methodologies resulted in a ranking of the capacity of sodium hyaluronate to bind in vitro to corneal surfaces.

Highlights

Dry Eye Disease (DED) is a common condition around the world that affects up to one in every three people [1]
In vitro corneal retention studies provide techniques that can provide further support within early formulation development and to classify mucoadhesive polymers [68], their mixtures and interactions of actives in ocular drug delivery. Both in vitro methodologies produced comparable evidence and rankings based on the determination of the rate of Na-HA binding to ocular surfaces in eye drops
Eye drop solutions enabled a higher extent of Na-HA binding than was observed in the Phosphate-buffered saline (PBS) control

Summary

Introduction

Dry Eye Disease (DED) is a common condition around the world that affects up to one in every three people [1]. Pain and transient visual impairment, mostly due to tear film instability or a change in its composition that leads to a disruption in the tear film [3]. The naturally occurring endogenous factor hyaluronate induces longlasting, intensive ocular lubrication [5], and this explains why several artificial tear solutions contain sodium hyaluronate (Na-HA) as a moisturizing and lubricating substance. Most molecular weights of the hyaluronates that are incorporated into eye drops vary or are unknown

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Conclusion