In-vitro and in-vivo evaluation of carrageenan/methylcellulose polymeric systems for transscleral delivery of macromolecules

In this study, polymeric dispersions composed of methylcellulose (MC) and either kappa carrageenan (KC) or iota carrageenan (IC) were proposed as a platform for transscleral delivery of macromolecules. The additive effects of the two polymers were investigated using oscillatory rheometer and FT-IR spectroscopy. Mechanical spectra demonstrated a conformation dependent association of the two polymers at 37 °C in the presence of selected counter ions. The polymer association was also confirmed by the shifts in MC peaks at 1049.5, 1114 and 1132.9 cm−1 in the presence of carrageenans, which corresponds to the stretching vibrations of C–O–C bonds of the polysaccharides. The MC–IC polymeric system displayed the highest bio-adhesion, owing to the relatively high negative charge. However, the MC–IC system did not affect the in-vitro scleral permeability of sodium fluorescein and 10 kDa FITC-dextran. Nonetheless, the formulation properties had a substantial impact on the results of the in-vivo studies. The efficacy of transscleral drug delivery was determined using rats with altered connexin 43 (Cx43) levels, a gap junction protein, in the choroid. Periocular injection of Cx43 antisense oligonucleotides (AsODN) incorporated in the MC–IC system lead to a significant reduction in the Cx43 levels in the choroid of rats at 24 h of treatment. AsODN incorporated in phosphate buffered saline (PBS) also demonstrated a trend towards reduced Cx43 levels; however this was not statistically significant owing to great variability between treated animals. Consequently the in-vivo data suggests the transscleral route to be of value in delivering therapeutics to the choroid. Moreover this study identified a new polymeric system based on MC and IC which provides aqueous loading of therapeutics and prolonged retention at the site of administration.

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