Transscleral diffusion of ethacrynic acid and sodium fluorescein

[摘要] Purpose: One of the current limitations in developing novel glaucomadrugs that target the trabecular meshwork (TM) is the induced cornealtoxicity from eyedrop formulations. To avoid the corneal toxicity, analternative approach would be to deliver TM drugs through the sclera. Tothis end, we quantified ex vivo diffusion coefficient of a potential TMdrug, ethacrynic acid (ECA), and investigated mechanisms of ECAtransport in the sclera.Methods: An Ussing-type diffusion apparatus was built to measure theapparent diffusion coefficient of ECA in fresh porcine sclera at 4 °C. To understand mechanisms of ECA transport, we quantified thetransscleral transport of a fluorescent tracer, sodium fluorescein(NaF), that has a similar molecular weight but is more hydrophiliccompared to ECA. Furthermore, we developed a mathematical model tosimulate the transport processes and used it to analyze the experimentaldata. The model was also used to investigate the dependence of diffusioncoefficients on volume fraction of viable cells and the binding of NaFand ECA to scleral tissues.Results: The diffusion coefficients of ECA and NaF in the sclerawere 48.5±15.1x10-7 cm2/s (n=9) and 5.23±1.93x10-7 cm2/s (n=8), respectively. Both diffusioncoefficients were insensitive to cell shrinkage caused by ECA during thediffusion experiments and cell damage caused by the storage of tissuesex vivo before the experiments. Binding of ECA to scleral tissues couldnot be detected. The apparent maximum binding capacity and the apparentequilibrium dissociation constant for NaF were 80±5 mM and 2.5±0.5 mM (n=3), respectively.Conclusions: These data demonstrated that ECA diffusion wasminimally hindered by structures in the sclera, presumably due to thelack of cells and binding sites for ECA in the sclera.

[学科分类] 生物化学/生物物理