Polyacrylic acid mediated ocular delivery of ribozymes

A catalytic RNA (ribozyme) was formulated with polyacrylic acid (Carbopol(R)) for ocular delivery in mice. In vitro experiments showed that the ribozyme could be loaded into the polymer in the gel state and be released from the polymer upon collapse of the gel by addition of cations. The ribozyme was formulated with polyacrylic acid and administered to mouse eyes. 5-10-fold greater retention of ribozyme was obtained compared to ribozyme alone. Further characterisation of the formulation showed greater ribozyme accumulation when applied as a liquid rather than a gel. Two independent methods were used to show that the ribozymes were internalized rather than adsorbed to the surface of the eye. The first involved the treatment of the mouse eyes with microccocal nuclease after ribozyme administration. Less than 50% of the ribozyme was removed by nuclease. The second method visualized ribozyme localization within the tissue by autoradiography using P-33-labeled ribozyme. The results showed that the ribozyme was localized in the outer layers of the corneal epithelium 10 min after administration. 30 min after administration, grains were localized over the lower epithelial layers and into matrix. The kinetics of ribozyme accumulation showed that uptake peaked 30 min after administration and the ribozyme levels persisted in the ocular tissue for 3 h after administration. Ocular retention of the ribozyme was linear over the dose range of 42-833 mu M with a constant 0.5% Carbopol(R) concentration, thus showing that the highest concentration of the ribozyme did not exceed the loading capacity of the polymer. These results demonstrate the potential for polyacrylic acid to be a controlled release drug delivery vehicle for ribozymes to epithelium.