Permeability characteristics of novel mydriatic agents using an in vitro cell culture model that utilizes sirc rabbit corneal cells

The purpose of this study was to evaluate the permeability characteristics of a previously reported in vitro corneal model that utilizes SIRC rabbit c orneal cells and to investigate the permeability of three novel esters of p henylephrone chemical delivery systems (CDS) under different pH conditions using this in vitro model. The SIRC rabbit corneal cell line was grown on t ranswell polycarbonate membranes, and the barrier properties were assessed by measuring transepithelial electrical resistance (TEER) using a voltohmme ter. The permeabilities of esters of phenylephrone CDS across the SIRC cell layers were measured over a pH range 4.0-7.4. The esters tested include ph enylacetyl (1), isovaleryl (2), and pivalyl (3). The SIRC rabbit corneal ce ll line, when grown on permeable filters, formed tight monolayers of high e lectrical resistance with TEER values increasing from 71.6 +/- 20.8 Ohm.cm( 2) at day 3 in culture to 2233.42 +/- 15.2 Ohm.cm(2) at day 8 in culture an d remained constant through day 14 in culture. The transepithelial permeabi lity coefficients (P-app) at pH 7.4 ranged from 0.58 x 10(-6) cm/s for the hydrophilic marker, mannitol, to 43.5 x 10(-6) cm/s for the most lipophilic molecule, testosterone. The P-app at pH 7.4 for phenylephrine was 4.21 x 1 0(-6) cm/s. The P-app values and the lag times of the three esters of pheny lephrone were pH dependent. The P-app for 1, 2, and 3 at pH 7.4 were 14.76 x 10(-6), 13.19 x 10(-6), and 12.86 x 10(-6) cm/s, respectively and the per meabilities decreased at conditions below pH 7.4. The lag times at pH 7.4 w ere 0.10, 0.17, and 0.12 h for 1, 2, and 3, respectively, and the values in creased at lower pH conditions. The TEER values of SIRC cell line observed at day 8 to day 14 in the present investigation are similar to the resistan ce value reported for rabbit cornea (2 k Ohm.m(2)). All the esters showed s ignificantly (p < 0.05) higher permeabilities than phenylephrine at pH 7.4. The rate and extent of transport of the drugs across the cell layers were influenced by the fraction of ionized and un-ionized species and the intrin sic partition coefficient of the drug. The results indicate that the permea bility of ophthalmic drugs through ocular membranes may be predicted by mea suring the permeability through the new in vitro cell culture model.