title: Mechanistic studies on the degradation and protein release characteristics of poly(lactic-co-glycolic-co-hydroxymethylglycolic acid) nanospheres.
abstract: The purpose of this study was to gain mechanistic insights into the effect of different formulation parameters on the degradation and release behavior of protein-loaded nanoparticulate carrier systems based on an aliphatic polyester with pendant hydroxyl groups, poly(lactic-co-glycolic-hydroxymethyl glycolic acid) (pLGHMGA). Bovine serum albumin (BSA) was used as a model protein. BSA-loaded pLGHMGA nanospheres of 400-700 nm were prepared using a solvent evaporation method using pLGHMGA of different molecular weights and different compositions. Also, the concentration of pLGHMGA in the organic phase was varied. The nanospheres showed a continuous mass loss accompanied by continuous decrease in number average molecular weight, which indicates that the degradation of the nanospheres is by bulk degradation with a rapid release of water-soluble low molecular weight fragments. On the basis of NMR analysis, it is concluded that intramolecular transesterification precedes extensive hydrolysis of the polymer and degradation of the nanospheres. BSA-loaded freeze-dried nanospheres showed a significant burst release of 40-50% of the BSA loading. In contrast, nonfreeze-dried samples showed a small burst of around 10-20%, indicating that freeze-drying induced pore formation. Nonlyophilized nanospheres prepared from pLGHMGA with 64/18/18 lactic/glycolic/hydroxymethylglycolic acid (L/G/HMG) ratio showed a relatively fast release of BSA for the next 30 days. Nanospheres prepared from a more hydrophobic pLGHMGA (74/13/13, L/G/HMG) showed a two-phase release. Circular dichroism analysis showed that the secondary structure of the released protein was preserved. This study shows a correlation between release behavior and particle erosion rate, which can be modulated by the copolymer composition.
authors: Department of Pharmaceutics, Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Utrecht, The Netherlands.
authors: N
authors: N
authors: Samadi
authors: C F
authors: CF
authors: van Nostrum
authors: T
authors: T
authors: Vermonden
authors: M
authors: M
authors: Amidi
authors: W E
authors: WE
authors: Hennink
mesh_terms: D000818:Animals; D002417:Cattle; D005612:Freeze Drying; D054118:Nanospheres / Q000737:chemistry*; D011091:Polyesters / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry; D012710:Serum Albumin, Bovine / Q000737:chemistry*
chemical_list: D011091:Polyesters; D011108:Polymers; C544675:poly(lactic-co-hydroxymethyl glycolic acid); D012710:Serum Albumin, Bovine