gms | German Medical Science

Objectives: In addition to biocompatibility, toxicology and pharmacology testing, the “Guideline on Human Cell Based Medicinal Products” of the “European Medicines Agency” demands standardized quality assurance procedures in large animals for the production of tissue engineering constructs. The present study thus aimed at evaluating such standardized quality parameters using chondral defects in sheep stifle joints.

Methods: Two full thickness cartilage defects (8 x 8 mm) were created on the load-bearing area of the right medial femur condyle of 9 merino sheep (female, 2-4 years old). The defects were either left uncovered (empty defects; control) or covered with a cell-seeded polyglycolic acid (PGA) implant (verum). After 6 months, the contralateral left knee was operated in an identical fashion and the animals were sacrified after 12 months. Thereafter, the mRNA expression for collagen 1, collagen 2, and aggrecan as the main proteoglycan was analyzed by RT-PCR in day 0, 6 month, and 12 month samples. For glycosaminoglycan (GAG) quantification, a dimethylene blue (DMB) assay of regenerate tissue was performed.

Results and Conclusion: In addition to a continuous and significant decrease of aggrecan mRNA over time in both controls and verum defects, the controls showed a 6 month significant peak of collagen 1 (30-fold over time point 0) and collagen 2 (365-fold) and a subsequent return to baseline levels. In contrast, verum defects displayed a continuous decrease of collagen 1 mRNA by 80% over time, as well as a 6 month peak (117-fold) and long-term increased expression (15-fold) of collagen 2. The GAG content in both controls and verum defects was significantly decreased after 6 months and thereafter numerically increased at 12 months.

Whereas uncovered control defects showed parallel, transient expression of dedifferentiation (collagen 1) and chondrogenesis markers (collagen 2) only at 6 months, MACT-covered verum defects displayed diminished expression of the dedifferentiation marker collagen 1 and long-term elevation of the chondrogenesis marker collagen 2, underlining the therapeutic potential of defect coverage with cell-seeded PGA implants.