Ex Vivo Pig Eye Model for Studying Diffusion of Acylcarnitines with Different Physicochemical Properties

To explore the diffusion capacities between the anterior and vitreous chambers in a novel ex vivo pig eye model using a mix of stable isotope-labeled acylcarnitines representing metabolites with different physical and chemical properties, and analysis using mass spectrometry (MS). Enucleated pig eyes were injected in the anterior or vitreous chamber of the eye with a stable isotope-labeled acylcarnitine mix (free carnitine, C2, C3, C4, C8, C12, and C16-having an increasing size and hydrophobicity in that order). Samples were collected from each chamber at 3, 6, and 24 h postincubation for analysis using MS. After injection into the anterior chamber, the concentration of all acylcarnitines increased in the vitreous chamber over the observation period. After injection in the vitreous chamber, the acylcarnitines diffused to the anterior chamber with the highest concentration observed at 3 h postinjection, followed by a decrease in concentration possibly due to an elimination from the anterior chamber despite continued diffusion from the vitreous chamber. C16, the most hydrophobic and longest chain molecule, showed slower diffusion in both experimental settings. We hereby show a distinct diffusion pattern of molecules with different molecular size and hydrophobicity within and between the anterior and vitreous chamber. This model can be useful for optimizing choices and design of therapeutic molecules with higher retaining or depot properties into the two chambers of the eye for future intravitreal, intracameral, and topical treatment purposes.