Molecular and cellular studies of hyaluronic acid-modified liposomes as bioadhesive carriers for topical drug delivery in wound healing

Liposomes, modified into bioadhesive systems by the covalent anchoring of hyaluronic acid (HA) to their surface, were investigated for their abilities to act as site-adherent and sustained-release carriers of drugs for the topical therapy of wounds and burns. Epidermal growth factor (EGF) served as the test drug for growth factors and monolayers of the A431 cell line served as models of the in vivo designated targets. The hyaluronic acid was radiolabeled to carry ³H, through a deacetylation-reacetylation procedure, yielding specific activities in the range of 1 × 10⁶ dpm/mg. The HA was bound to the surface of the liposomes, using carbodiimide to crosslink its carboxyl residues to amine residues at the liposomal surface. The latter was provided through the inclusion of phosphatidylethanolamine in the liposome formulation. Varying the initial HA/lipid ratio over the range 1-500 mg HA/mmol lipid, it was found that the increase in bound HA was linear, providing up to 80 mg HA/mmol lipid. The HA-modified, but not the nonmodified, liposomes were found to bind with high affinity (ΔG° in the range of -7 to -9 Kcal/mol) to monolayers of the A431 cell line. The HA-modified liposomes were found to encapsulate EGF at high yields (% encapsulation, >87) and to act as sustained-release depots, the rate constant for the release of the encapsulated EGF in the range of 1.4 × 10^-3 h^-1. Taking all of these findings together, it is concluded that these liposomes are bioadhesive sustained-release carriers of drugs, as desired, meriting further cellular and in vivo studies.