Stability of proteins encapsulated in injectable and biodegradable poly(lactide-co-glycolide)-glucose millicylinders.
OBJECTIVE
To characterize protein stability in poly(lactide-co-glycolide) 50/50-glucose star (PLGA-Glu) injectable millicylinders and to compare results with linear PLGA 50/50.


METHODS
Bovine serum albumin (BSA), a model protein, was encapsulated in PLGA-Glu and linear PLGA millicylinders by solvent-extrusion and incubated under physiological conditions. Important system properties were characterized, including: polymer molecular weight distribution, soluble acidic residues, polymer morphology, polymer water uptake, microclimate pH, protein content and release, and protein aggregation. The polymer microclimate late in the release incubation was simulated and protein recovery was analyzed by UV280, size exclusion chromatography, amino acid analysis, and a modified Bradford assay.


RESULTS
PLGA-Glu contained higher levels of low molecular weight oligomers, more rapidly biodegraded, and exhibited a lower microclimate pH than the linear 50/50 PLGA, which is the most acidic type in the PLGA family. BSA, when encapsulated in PLGA-Glu millicylinders, underwent extensive noncovalent insoluble aggregation over 2 weeks in vitro release, which was almost completely inhibited upon co-encapsulation of Mg(OH)2. However, by 5 weeks release for base-containing formulations, although insoluble aggregation was still suppressed, the soluble fraction of protein in the polymer was unrecoverable by the modified Bradford assay. Polymer microclimate simulations with extensive protein analysis strongly suggested that the low recovery was mostly caused by base-catalyzed hydrolysis of the oligomeric fraction of BSA.


CONCLUSIONS
In PLGA-Glu, the acidic microclimate was similarly responsible for insoluble aggregation of encapsulated BSA. BSA aggregation was inhibited in millicylinders by co-incorporation into the polymer an insoluble base, but over a shorter release interval than linear PLGA likely because of a more acidic microclimate in the star polymer.
Kang
Jichao
J
Department of Pharmaceutical Sciences, University of Michigan, 428 Church St., Ann Arbor, MI 48109-1065, USA.
Lambert
Oliver
O
Ausborn
Michael
M
Schwendeman
Steven P
SP
D004339:Drug Compounding; D004355:Drug Stability; D005079:Excipients; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D019344:Lactic Acid / Q000737:chemistry*; D008276:Magnesium Hydroxide / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D008970:Molecular Weight; D053758:Nanoparticles; D011100:Polyglycolic Acid / Q000737:chemistry*; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011199:Potentiometry; D011506:Proteins / Q000008:administration & dosage* / Q000737:chemistry*; D012710:Serum Albumin, Bovine / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D014867:Water / Q000032:analysis
D005079:Excipients; D011506:Proteins; D014867:Water; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D012710:Serum Albumin, Bovine; D019344:Lactic Acid; D008276:Magnesium Hydroxide