Development and In Vitro Characterization of Liposomes Coated with Thiolated Poly(Acrylic Acid) for Oral Drug Delivery

Abstract

Mucoadhesive drug delivery systems offer promising opportunities for oral drug delivery. The aim of this study was to investigate the feasibility of preparing liposomes that are coated with the multifunctional polymer poly(acrylic acid)-cysteine (PAA-Cys). Cationic multilamellar vesicles (MLV) as well as cationic submicron-sized liposomes (ssLip) were prepared and coated with PAA-Cys. Size, zeta potential, amount of free thiol groups, aggregation behavior, drug-loading, and drug release of these novel carriers were evaluated. A switch of the initial positive zeta potential to a negative value after coating indicated the successful coating procedure. In both size ranges, MLV and ssLip, the amount of free thiol groups was comparable to that in a PAA-Cys solution of the same concentration. Drug loading of the hydrophilic marker fluorescence-isothiocyanate 4 kDa (FD4) was higher in PAA-Cys liposomes in comparison to noncoated liposomes, but lower in comparison to liposomes coated with unmodified poly(acrylic acid) (PAA). Only a minor ssLip or no increase MLV of the drug-loading was observed when using carboxyfluorescein (CF). These effects were attributed to interactions between the markers and the poly(acrylates). Coating of liposomes with PAA-Cys and PAA did not influence the release profile of FD4 and CF, whereas the release profile was affected by the molecular mass of the marker and the liposome size. In conclusion, the feasibility of coating liposomes with PAA-Cys was demonstrated, and it could be shown that this novel carrier system fulfills the basic requirements for an intended use in oral drug delivery.