(499a) Protein Adsorption on Biodegradable Polyanhydride Microspheres

In the past few decades, many efforts have focused on the study of biodegradable polymer microparticles (µPs) as effective drug carries with the purpose of developing protein delivery vehicles and single dose vaccines. In this context, polyanhydrides have shown to provide the right environment for protein stability and release. These surface-erodible chemistries have been shown to maintain the primary, secondary and tertiary structures of different proteins (i.e., ovalbumin, lysozyme, and tetanus toxoid), as well as their biological activity. In addition, in vitro release studies have showed that it is possible to control the release kinetics of proteins, ranging from days to months, by choosing the appropriate polyanhydride chemistry.

The biodistribution and biocompatibility of these carriers, and therefore their effectiveness as vaccine adjuvants, can be influenced by the adsorption of serum proteins in vivo; once µPs are administrated intravenously, they will first interact with plasma proteins. It has been suggested that adsorption of plasma proteins on the surface of microspheres can affect the release kinetics profiles provided by the microspheres. Particle surface properties (i.e.. hydrophobicity) play an important role in the amount of protein adsorbed. For this study, polymers based on sebacic acid (SA), 1,6-bis(p-carboxyphenoxy)hexane (CPH), and 1,8-bis(p-carboxyphenoxy)-3,6-dioxaoctane (CPTEG) anhydrides were synthesized. Cryogenic atomization method was used to fabricate microspheres based on CPH:SA and CPTEG:CPH that were characterized by SEM. Three model proteins from bovine serum plasma were chosen to study in vitro protein adsorption: bovine serum albumin (BSA), which is the most abundant protein in plasma; Immunoglobulin G (IgG), which is known to be an opsonin; and Fibrinogen (Fib), which in spite of its opsonization properties is considered a ?sticky? protein. Interaction between these proteins and µPs was studied by X-Ray Photoelectron Spectroscopy (XPS) and SDS-PAGE. In addition, confocal microscopy was used to observe the distribution of adsorbed BSA-FITC and IgG-Cy5 on the surface of polyanhydride µPs. Differences in the amount of protein adsorbed were detected ass a function of: (i) copolymer composition, and (ii) the specific protein studied. A direct correlation was observed between polymer hydrophobicity and protein adsorbed. On the other hand, higher quantities of Fib and IgG were absorbed on the µPs. In vitro release studies were performed with ovalbumin (Ova)-encapsulated microspheres that were then incubated with fibrinogen; the results obtained from SDS-PAGE showed a reduction in the amount of Ova released from the microspheres when Fib is adsorbed on the surface.

It is important to considerer that the adsorption of plasma proteins can affect the in vivo behavior of these polymeric devices in different ways. For example, it has been suggested that the presence of opsonins like immunoglobulin G and fibrinogen can accelerate the uptake of these microparticles by phagocytes; while the presence of serum albumins can maintain the circulation of these carriers for longer periods of time after i.v. administration. Therefore, determination and knowledge of protein adsorption patterns may be useful to understand and optimize the in vivo performance of these drug delivery devices.