Mapping microclimate pH distribution inside protein-encapsulated PLGA microspheres using confocal laser scanning microscopy.

ABSTRACT: The pH in the aqueous pores of poly(lactide-co-glycolide) (PLGA) matrix, also referred to as microclimate pH (?pH), is often uncontrolled, ranging from highly acidic to neutral pH range. The ?pH distribution inside protein-encapsulated PLGA microspheres was quantitatively evaluated using confocal laser scanning microscopy. The fluorescent response of Lysosensor yellow/blue dextran used to map ?pH in PLGA was influenced by the presence of encapsulated protein. The nonprotonated form of pyridyl group on the fluorescence probe at neutral pH was responsible for the interference, which was dependent on the type and concentration of protein. A method for correction of this interference based on estimating protein concentration inside the microspheres was established and validated. After correction of the influence, the ?pH distribution kinetics inside microspheres was evaluated for different PLGA 50/50 microsphere formulations under physiological conditions for 4 weeks. Generally, the ?pH acidity increased with the progression of incubation time. The coincorporation of poorly soluble base, magnesium carbonate, in the microspheres prolonged the appearance of detectable acidity for up to 3 weeks. Co-addition of an acetate buffer was able to control the ?pH over a slightly acidic range (around pH 4.7) after two week incubation. Microspheres prepared from a lower polymer concentration exhibited a higher ?pH, likely owing to reduced diffusional resistance to acidic degradation products. The stability of protein was enhanced by addition of MgCO(3), acetate buffer, or by reduced polymer concentration in the preparation, as evidenced by more soluble protein recovered after incubation. Hence, the ?pH imaging technique developed can be employed in the future for optimization of formulation strategies for controlling ?pH and stabilizing encapsulated proteins.

SUBMITTER: Liu Y 

PROVIDER: S-EPMC3817562 | biostudies-literature | 2012 May

REPOSITORIES: biostudies-literature