Optimization of hyaluronan-based eye drop formulations

Abstract

Hyaluronan (HA) is frequently incorporated in eye drops to extend the pre-corneal residence time, due to its viscosifying and mucoadhesive properties. Hydrodynamic and rheological evaluations of commercial products are first accomplished revealing molecular weights varying from about 360 to about 1200kDa and viscosity values in the range 3.7-24.2mPa s. The latter suggest that most products could be optimized towards resistance to drainage from the ocular surface. Then, a study aiming to maximize the viscosity and mucoadhesiveness of HA-based preparations is performed. The effect of polymer chain length and concentration is investigated. For the whole range of molecular weights encountered in commercial products, the concentration maximizing performance is identified. Such concentration varies from 0.3 (wt%) for a 1100kDa HA up to 1.0 (wt%) for a 250kDa HA, which is 3-fold higher than the highest concentration on the market. The viscosity and mucoadhesion profiles of optimized formulations are superior than commercial products, especially under conditions simulating in vivo blinking. Thus longer retention on the corneal epithelium can be predicted. An enhanced capacity to protect corneal porcine epithelial cells from dehydration is also demonstrated in vitro. Overall, the results predict formulations with improved efficacy.

Useful In Vitro Techniques to Evaluate the Mucoadhesive Properties of Hyaluronic Acid-Based Ocular Delivery Systems

“…In the 3D model the results show that the application of all three formulations obtained over 100% cell viability, meaning that the application of these MD provided a more suitable environment for cell proliferation. These results are very similar to the one performed by Salzillo et al where it was performed a study of cellular response of primary porcine corneal epithelial cells when administrated different HA formulations [18]. They justified their results with the hypothesis that the protective effect displayed by the HA formulation on the cells is related to the polymer’s water retaining capacity.…”

“…The crossover is the point of passage where the formulation stops presenting fluid-like characteristics and behaves more gel-like. The shear moduli present greater values in HA 0.30% in comparison with HA 0.15%, an indication that the strength of the formulation/mucin interaction increases with HA concentration [18,22]. …”

“…For a mucoadhesive polymer, which is the case of HA, the η muc+Ha is higher than (η muc + η HA ) due to the interactions occurring between the polymer and mucin. The mucoadhesive index is a measure of the mucoadhesive strength [18]. …”

“…The protective effect of the selected formulas against dehydration was evaluated using previously reported protocols, with modifications [18]. Specifically, cells were seeded in 24-well plates (5 × 10 4 cells/well) and in DMEM/F12 until 70% confluence was reached.…”

“…The most common and suitable methods to assess the mucoadhesive properties of a potential formulation candidate for ocular delivery is through in vitro techniques. Previous publications used simple methods which includes rheological techniques, particularly flow and oscillation methods and more sophisticated methods such as tensile strength measurements [16,17,18,19,20]. In vitro cell viability and morphology tests are also useful techniques to evaluate the efficacy of the product, studying the reaction of ocular cell lines, such as corneal epithelium HCE-T (Human Corneal Epithelial cells-Transformed) or ARPE-19 (Adult Retinal Pigment Epithelial cell line-19) cell lines, when exposed to the product [21].…”