of Recent and Current Projects: ? ? (1) Magnetic Resonance Imaging (MRI) of Drug Movement in the Eye: A number of inflammatory and neoplastic diseases of the eye are currently treated by repeated intravitreal drug injections. Transscleral delivery has emerged as a more attractive method for treating retinal disorders, because it offers localized delivery of drugs as a less invasive method compared to intravitreal administration. Numerous novel transscleral drug delivery systems, ranging from microparticles to implants, have been reported. However, transscleral delivery is currently not as clinically effective as intravitreal delivery in the treatment of retinal diseases, and this lack of success must be evaluated. Transscleral drug delivery systems require drugs to permeate through several layers of ocular tissue (sclera, choroid-Bruchs membrane, retinal pigment epithelium) to reach the neuroretina. In addition, clearance of administered drugs occurs by uptake into the conjunctival and choroidal blood and possibly into lymph. The initial phase of this study was aimed at gaining a better understanding of the clearance mechanisms in the eye so that better delivery methods could be designed. We used MRI as a non-invasive, in vivo method to track the movement of small and large molecule drug surrogates in the form of the MRI-tracers Gd-DPTA and Gd-albumin. The delivery of these agents was by bolus injection or by slow continuous infusion either into the subconjunctival or intra-scleral space of the eyes of anesthetized rabbits. ? The next phase of the MRI work on this project involves the use of an injectable, thermo-setting gel (ReGel) that would allow the sustained transscleral release of a protein to the eye. First, Gd-albumin will be used as an MRI marker test protein to study the time course of protein distribution in rabbits by the gel delivery method. Then, pigment epithelial derived factor (PEDF), a therapeutic protein comparable in size to albumin, will be delivered by the same method and its therapeutic effects will be studied in a rabbit. To measure the therapeutic effectiveness of PEDF in the eye with this delivery strategy, we will use an acute ischemic reperfusion model in the rabbit eye. The efficacy of PEDFs regression of the induced retinal ischemic damage will be monitored by ERG. More information about ReGel is described in the project below. ? . ? (2) Sustained-Release Devices for Intraocular Drug Delivery: We have investigated the use of sustained drug release devices that could release drugs into the body for periods as long as months. Recently, we tested the use of a thermosetting polymer, ReGel (Protherics, Inc.), as an injectable agent for long term release of drugs into the eye. This technique would eliminate the need for frequent invasive bolus liquid injections. Our experiments used subconjunctival injections of ReGel containing fluorescently labeled ovalbumin into rat eyes. In a subsequent phase of the project, we will test ReGel injections of Gd-albumin into rabbit eyes for MRI monitoring, as described above. In the rat experiments, a drug marker, in the form of fluorescently-labeled ovalbumin (Alexafluor-ova), was incorporated into the ReGel solution, which is liquid at room temperature. It was then injected into the subconjunctival space of rats, where it formed a slow releasing gel at 37 centigrade. Animals were sacrificed at serial time points from one hour up to 14 days and the enucleated eyes were examined in histological sections by fluorescent microscopy and by tissue extraction for the quantitative assessment of fluorescent labeled protein. Our data indicates that we obtained measurable levels of intact Alexa-ova for up to 14 days in sclera, choroid, and retina tissues using the ReGel system. ? ? (3) Influence of Proteoglycans on Axonal Growth: Chondroitin sulfate proteoglycans (CSPGs) are major components of glial scars that form soon after spinal chord injury. It is believed that CSPGs significantly inhibit axonal growth and regeneration. CSPGs consist of a protein core with large glycosaminoglycan (GAG) sugar side chains. Removal of the GAG chains by chondroitinases has been shown to restore neuronal growth activity. We are seeking to determine which of the specific GAG sugars, chondroitin sulfate A or chondroitin sulfate C, is responsible for the neuronal inhibition. We are also planning to study potential sustained release devices that can release the chondroitinases into the injury sites to reduce the presence of the GAG sugars on the proteoglycans and thus encourage axonal regeneration. ? Our initial experiments studied the effects of whole CSPGs on neuronal growth. We determined the release and distribution characteristics of nanoparticle-encapsulated CSPGs through a collagen test matrix. The effect of the CSPGs on the sprouting of PC-12 cells which were imbedded in the collagen matrix was measured. Cell growth and sprouting was monitored by confocal microscopy. We found a dose response in which cell growth was inhibited more at radial distances closer to the nanoparticle injection site where CSPG concentration would be the highest. ? The next phase of the project proposes a series of in vitro experiments to study the effects of the specific CSPG sugars on the growth and sprouting of neuronal PC-12 cells into a collagen matrix. Cell growth will be monitored by microscopy. In addition, we will test the release and distribution of chondroitinase enzyme which will be delivered from nanoparticles into the center of an in vitro gel matrix. The effectiveness of this delivery method on cleaving the inhibiting sugar moieties will be studied by monitoring of the inhibition of neuronal cell growth with confocal microscopy. Subsequent in vivo experiments would investigate the effectiveness of a nanoparticle enzyme delivery system on enhancing nerve regeneration by administering enzyme injections into rat spinal chord after chord injury.
| Kim, Stephanie H; Csaky, Karl G; Wang, Nam Sun et al. (2008) Drug elimination kinetics following subconjunctival injection using dynamic contrast-enhanced magnetic resonance imaging. Pharm Res 25:512-20 |
| Kim, Stephanie H; Galban, Craig J; Lutz, Robert J et al. (2007) Assessment of subconjunctival and intrascleral drug delivery to the posterior segment using dynamic contrast-enhanced magnetic resonance imaging. Invest Ophthalmol Vis Sci 48:808-14 |
| Robinson, Michael R; Lee, Susan S; Kim, Hyuncheol et al. (2006) A rabbit model for assessing the ocular barriers to the transscleral delivery of triamcinolone acetonide. Exp Eye Res 82:479-87 |
| Kim, Hyuncheol; Csaky, Karl G; Gravlin, Luisa et al. (2006) Safety and pharmacokinetics of a preservative-free triamcinolone acetonide formulation for intravitreal administration. Retina 26:523-30 |
| Kim, Hyuncheol; Csaky, Karl G; Chan, Chi-Chao et al. (2006) The pharmacokinetics of rituximab following an intravitreal injection. Exp Eye Res 82:760-6 |
