title: BSA degradation under acidic conditions: a model for protein instability during release from PLGA delivery systems.
abstract: Acidification of the internal poly(lactide-co-glycolide) (PLGA) microenvironment is considered one of the major protein stresses during controlled release from such delivery systems. A model protein, bovine serum albumin (BSA), was incubated at 37 degrees C for 28 days to simulate the environment within the aqueous pores of PLGA during the release phase and to determine how acidic microclimate conditions affect BSA stability. Size-exclusion high performance liquid chromatography (SE-HPLC), SDS-PAGE, and infrared spectroscopy were used to monitor BSA degradation. BSA was most stable at pH 7, but rapidly degraded via aggregation and hydrolysis at pH 2. These simulated degradation products were nearly identical to that of unreleased BSA found entrapped within PLGA 50/50 millicylinders. At pH 2, changes in BSA conformation detected by various spectroscopic techniques were consistent with acid denaturation of the protein. By contrast, at pH 5 and above, damage to BSA was insufficient to explain the instability of the protein in the polymer. Thus, these data confirm the hypothesis that acid-induced unfolding is the basis of BSA aggregation in PLGA and the acidic microclimate within PLGA is indeed a dominant stress for encapsulated BSA. To increase the stability of proteins within PLGA systems, formulations must protect against potentially extreme acidification such that native structure is maintained.
authors.affiliation: Department of Pharmaceutical Sciences, School of Pharmacy, Center for Pharmaceutical Biotechnology, University of Colorado Health Sciences Center, Denver, 80262, USA.
authors.forename: Tia
authors.initials: T
authors.lastname: Estey
authors.forename: Jichao
authors.initials: J
authors.lastname: Kang
authors.forename: Steven P
authors.initials: SP
authors.lastname: Schwendeman
authors.forename: John F
authors.initials: JF
authors.lastname: Carpenter
mesh_terms: D016503:Drug Delivery Systems; D004355:Drug Stability; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000737:chemistry*; D011100:Polyglycolic Acid / Q000737:chemistry*; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011108:Polymers / Q000737:chemistry*; D011489:Protein Denaturation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012710:Serum Albumin, Bovine / Q000737:chemistry*
chemical_list: D011108:Polymers; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D012710:Serum Albumin, Bovine; D019344:Lactic Acid