(T1330-07-38) Impact of Oleic Acid Based Nanoemulsions on Corneal Integrity: An Ex Vivo Study Using Rabbit Corneas

Purpose: Oleic acid is a monounsaturated fatty acid used in drug delivery systems because of its biocompatibility, ability to enhance drug solubility, and capacity to improve the permeability of drugs across biological membranes. In the context of ocular drug delivery, oleic acid can be incorporated into nanoemulsions (NEs) to improve drug loading as well as the transcorneal permeation of drugs, thereby enhancing their therapeutic efficacy. However, its effect on the corneal integrity at concentrations greater than 0.1% has not been studied. This research work aimed to investigate the effect of oleic acid on the corneal integrity and paracellular and transcellular pathways, ex vivo, using two markers, namely acyclovir (paracellular marker) and moxifloxacin (transcellular marker).

Methods: Oil-in-water NEs containing 2.5%, 5%, and 7.5% w/v of oleic acid were prepared using hot homogenization at a temperature of 65±1ºC using a T25 digital Ultra-Turrax disperser followed by probe sonication using Sonics Vibra-Cell™ Sonicator. The NEs were then characterized by employing dynamic light scattering, electrochemical measurement, and freeze-point depression techniques. Additionally, the NEs were evaluated for histological studies using New Zealand White rabbit corneas, and transcorneal permeation through paracellular and transcellular routes using a vertical Franz diffusion apparatus.

Results: The 2.5% w/v oleic acid-based NE showed a droplet size (DS), a polydispersity index (PDI), and a zeta potential (ZP) of 101.0±0.9 nm, 0.21±0.01, -25.2±0.2 mV, respectively, while the 5% and 7.5% w/v oleic acid-based NEs showed a DS of 125.6±1.1 and 157.1±3.5 nm, a PDI of 0.21±0.01 and 0.20±0.01, and a ZP of -27.0±0.4 and -33.6±1.5 mV, respectively. The pH and osmolality values were favorable for topical ocular application. Histological studies revealed no evidence of tissue damage upon exposing the corneas to these concentrations of oleic acid for up to 3 hours (Fig.1). The transcorneal permeation studies indicated that transcorneal flux and permeability coefficients of the transcellular marker increased as a function of oleic acid concentration. Oleic acid, however, did not have a significant (p > 0.05) effect on the permeation of the paracellular marker.

Conclusion: The data suggests that oleic acid can be safely used up to 7.5% w/v without disrupting the corneal integrity, while also serving as an effective transcellular permeation enhancer, thus increasing ocular bioavailability of drugs with poor solubility and membrane permeability characteristics. In vivo studies are required to evaluate the ocular irritation and cellular toxicity of oleic acid at the studied concentrations.

Figure 1. Histology of corneas isolated from New Zealand White rabbit eyeballs after a 3-hour exposure to DPBS or nanoemulsion formulations containing three different concentrations of oleic acid (n=3, 20x).