No abstract

Articular cartilage lesions that do not disrupt the integrity of subchondral bone are not capable of spontaneous repair. The asymptomatic nature of these lesions leads to articular cartilage degeneration and development of the osteoarthritic process. To avoid joint replacement surgery, several cellular therapies have been developed. These therapies focus on the regeneration of a new tissue, whose structure, biochemistry composition and function should be the same as those of endogenous articular cartilage. Current approaches for interrupting the osteoarthritic process produce a fibrocartilaginous tissue, not articular cartilage. The implantation of autologous chondrocytes and autologous mosaicplasty induces a better quality of articular cartilage; however, both techniques damage the existing cartilage because of the need to harvest large numbers of chondrocytes or to extract an osteochondral cylinder for implantation. While stem cells are a promising tool for repairing articular cartilage, their use is in an early experimental stage at this time. Although studies of cell therapy have shown clinical and functional improvement in joints, the ability to regenerate articular cartilage that resists the degeneration process remains elusive.

proteoglycan content was found decreased by histomorphometry (score decline-64%) and biochemical analysis of GAG (-75%) and total collagen (-30%) content. Gene expression of catabolic enzymes (MMP13, MMP1, MMP2), and genes involved in inflammatory response (IL8, CCL2, CCL4 CXCL2) was significantly increased (>4-fold) and genes related to ECM formation (COL2A1, COMP, Aggrecan, COL8A1, COL11A1) were decreased (<-4-fold). Whereas histological and biochemical characteristics of the TNF-alpha induced model match with observations known from human OA cartilage, gene expression analysis revealed contrary gene expression pattern related to ECM formation (COL2A1, COL11A1, COMP) and to hypertrophic bone formation (COL10A1). The addition of TGF-b1 and PRP during TNF-alpha stimulation led to reduced GAG loss (both 40%) whereas IL1b enhanced the GAG loss by further 10% demonstrating responsiveness of the model to test substances. Conclusions: The use of porcine chondrocytes in micromasses and the addition of TNF-alpha resulted in the induction of some typical features of OA such as extensive ECM loss and induction of genes related to catabolic activity and inflammatory response. In contrast to human OA, ECM formation was inhibited, which might be a consequence of the exclusive use of TNF-alpha, which is only one of many impacting factors in OA. Although not all characteristics of human OA could be demonstrated, the presented test system was suitable to detect effects of test substances. TNF-alpha induced porcine micromasses can be a useful supplement to existing preclinical tests in OA and an alternative to the use of human tissue in vitro.