Effect of cyclodextrins on α-chymotrypsin stability and loading in PLGA microspheres upon S/O/W encapsulation

The potential of cyclodextrins to stabilize alpha-chymotrypsin upon encapsulation in Poly(lactic-co-glycolic) acid (PLGA) microspheres using a solid-in-oil-in-water (s/o/w) technique was investigated. Two cyclodextrins, hydroxyl-propyl-beta-cyclodextrin (HP beta CD) and methyl-beta-cyclodextrin (M beta CD), one insoluble and the other soluble in methylene chloride, were used. The results demonstrate that HP beta CD failed to stabilize alpha-chymotrypsin upon encapsulation. Specifically, 19% of the protein was aggregated and the specific activity of the enzyme was reduced to ca. 50% of that prior to encapsulation. In contrast, M beta CD significantly decreased the formation of aggregates to 3% and the retained specific activity of the enzyme was approximately 90%. The co-lyophilization of alpha-chymotrypsin with M beta CD prior to encapsulation was a requisite to preserve the protein stability in microspheres. Furthermore, M beta CD prevented the loss of protein during the preparation of microspheres and the encapsulation efficiency was improved to 90%. Release experiments showed the use of M beta CD modified the release profile: the burst release decreased from 54% (in the absence of the excipient) to 36%. The results suggest that M beta CD might be a suitable excipient to improve protein stability in s/o/w encapsulation procedures. (C) 2006 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 95:849-858, 2006.