BMP-7-Loaded PGLA Microspheres as a New Delivery System for the Cultivation of Human Chondrocytes in a Collagen Type I Gel: The Common Nude Mouse Model

Abstract

Bone morphogenic protein 7 (BMP-7) released from polylactide (PLGA) microspheres has proven to be a potent system in cartilage tissue engineering in vitro. However, in vivo data are still lacking. The aim of this study was to investigate this BMP-7 release system utilizing the nude mouse as a small animal model. Human osteoarthritic chondrocytes of 10 patients were enzymatically released and transferred into a collagen type-I gel. A concentration of 2x10(5) cells/mL was used. BMP-7 encapsulated in PGLA microspheres was added at an initial concentration of 500 ng BMP-7/mL gel. Untreated specimens and specimens with empty microspheres served as control. Samples were cultivated subcutaneously in nude mice for 6 weeks. After recovery, chondrocytes of all groups displayed a spheroid morphology without signs of dedifferentiation. The proteoglycan and collagen type II content of the control groups was restricted to the immediate pericellular region, whereas treatment group samples showed enhanced collagen type II production. Collagen type II and aggrecan gene expression was enhanced in treatment group samples with respect to the two control groups (mean +/- SD: 0.268 +/- 0.450 to 0.152 +/- 0.129 and 0.155 +/- 0.216 ng/ng beta-actin for collagen type II; 0.535 +/- 0.731 to 0.367 +/- 0.651 and 0.405 +/- 0.326 ng/ng beta-actin for aggrecan), whereas collagen type I gene expression decreased by a factor of 10. Relative protein quantification of collagen type II, collagen type I and proteoglycan was in accordance. Our data suggest that BMP-7 release from PGLA microspheres led to an improved tissue-engineered cartilage analogue in vivo with an increase in hyaline-cartilage-specific components.