Research paper Development and characterization of CyA-loaded poly(lactic acid)± poly(ethylene glycol)PEG micro- and nanoparticles. Comparison with conventional PLA particulate carriers Ruxandra Gref a, * , Patricia Quellec b , Alejandro Sanchez c , Pilar Calvo c , Edith Dellacherie b , Maria J. Alonso c a School of Pharmacy, University of Paris Sud, Cha Ãtenay Malabry, France b ENSIC-LCPM, Nancy, France c Department of Pharmaceutical Technology, School of Pharmacy, University of Santiago de Compostela, Santiago de Compostela, Spain Received 12 July 2000; accepted 5 October 2000 Abstract Cyclosporin A (CyA) loaded poly(lactic acid)±poly(ethylene glycol) (PLA±PEG) micro- and nanoparticles have been developed using an emulsion-solvent evaporation method. Physico-chemical properties, peptide loading content and in vitro release pro®les of these novel CyA carriers were compared with those corresponding to conventional PLA micro- and nanoparticles. Results obtained con®rm the previously described disposition of PEG chains on the surface of the PLA±PEG formulations. In addition, they revealed the presence of CyA molecules on the surface of both PLA and PLA±PEG systems. Further determination of the surface chemical composition by electron spectroscopy for chemical analysis (ESCA) allowed us to quantify the amount of CyA in the nanospheres' top layers, this amount being higher for nanoparticles than for microparticles, and higher for the PLA systems than for those based on PLA±PEG. In vitro release experiments revealed that PLA±PEG particles provided a more adequate control of CyA release than conventional PLA micro- and nanoparticles. Physico-chemical characterization of the systems during the release studies showed that the developed PLA and PLA±PEG micro- and nanoparticles were not degraded, which suggest a diffusion-mediated release mechanism. Furthermore, we have hypothesized that the hydrophilic outer shell of PEG provides a stationary layer for the diffusion of CyA. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Poly(lactic acid); Poly(lactic acid)±poly(ethylene glycol); Microparticle; Nanoparticle; Controlled release; Cyclosporin A; Peptide delivery 1. Introduction Previous reports have described the ability of nanoparti- cles made of block copolymers of poly(ethylene glycol) (PEG) and poly(lactic acid) (PLA) or poly(lactic-co-glyco- lic acid) (PLGA) to extend the blood circulation times of bioactive materials by diverting them away from the mono- nuclear phagocytic system (MPS) [1,2]. Therefore, the development of these Stealth nanoparticles has been initi- ally focused to provide targeted delivery after intravenous administration. Nevertheless, recent reports have shown the attractive features of PLA±PEG micro- and nanoparticles as new protein delivery systems for oral and nasal admin- istration [3,4]. Compared with conventional particulate carriers (i.e. PLA micro- and nanoparticles), PLA±PEG- based systems have shown improved stability in the gastro-intestinal (GI) tract, thus favouring the protein trans- port through the intestinal barrier. An additional feature of these systems includes their speci®c disposition to reach the lymphatic system after oral and nasal administration and, consequently, their great potential for the delivery of proteins to the lymphatic system. These interesting properties provide new therapeutic opportunities and open up viable possibilities to improve conventional therapies. Cyclosporin A (CyA) is an example of a peptide which can bene®t from the above-mentioned features. This highly hydrophobic peptide is used in the prevention of xenograft rejection following organ transplan- tation and it is also applied in the treatment of patients with selected autoimmune diseases [5]. However, it is well known that CyA presents a major problem related to its highly vari- able and incomplete absorption from its conventional oral European Journal of Pharmaceutics and Biopharmaceutics 51 (2001) 111±118 0939-6411/00/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S0939-6411(00)00143-0 www.elsevier.com/locate/ejphabio * Corresponding author. School of Pharmacy, University of Paris Sud, UMR CNRS 8612, Cha Ãtenay Malabry, France. Tel.: 133-146-835581; fax: 133-146-619334. E-mail address: ruxandra.gref@cep.u-psud.fr (R. Gref).