FTIR characterization of the secondary structure of proteins encapsulated within PLGA microspheres'

A commonly used technique for protein encapsulation in microspheres is the double-emulsion method wherein an initial water-in-oil (w/o) emulsion of pr otein and polymer is formed via sonication, and then a second emulsion (w/o )/w is formed by dispersion in an aqueous phase via homogenization. This ap proach is often used to produce microspheres of biodegradable poly(lactic-c o-glycolic acid) (PLGA). The harsh processing associated with this method c an cause denaturation of the encapsulated protein. Herein, we have used Fou rier transform infrared (FTIR) spectroscopy to determine the secondary stru ctures of two model proteins, bovine serum albumin (BSA) and chicken egg-wh ite lysozyme, within PLGA microspheres. The alpha-helix content of both pro teins in the microspheres was about a third lower than in the lyophilized s tate, indicating conformational changes upon protein entrapment within the microspheres. BSA microspheres containing the stabilizing excipient trehalo se have a higher alpha-helix content than those without excipient, suggesti ng that trehalose partially prevents the denaturing effects incurred during processing. In addition, BSA released from microspheres is improved by inc orporation of trehalose: analysis of the protein released from the microsph eres indicates that there is less BSA dimer formation in the trehalose-cont aining microspheres than in those without trehalose. (C) 1999 Elsevier Scie nce B.V. All rights reserved.