Comparison of the Effects of Interleukin-1 on Equine Articular Cartilage Explants and Cocultures of Osteochondral and Synovial Explants

Abstract

Osteoarthritis (OA) is a ubiquitous disease affecting many horses. The disease causes chronic pain and decreased performance for patients and great cost to owners for diagnosis and treatment. The most common treatments include systemic non-steroidal anti-inflammatory drugs and intra-articular injection of corticosteroids. There is excellent support for the palliative pain relief these treatments provide; however, they do not arrest progression and may in some instances hasten advancement of disease. Orthobiologic treatments have been investigated as potential OA treatments that may not only ameliorate pain but also prevent or reverse pathologic articular tissue changes. Clinical protocols for intra-articular use of such treatments have not been optimized; the high cost of in vivo research and concerns over humane use of research animals may be preventing discovery. The objective of this study was to evaluate a novel in vitro articular coculture system for future use in OA treatment research. Concentrations and fold increases in various markers of inflammation (prostaglandin E₂ and tumor necrosis factor-alpha), degradative enzyme activity [matrix metalloproteinase-13 (MMP-13)], cartilage and bone metabolism (bone alkaline phosphatase and dimethyl-methylene blue), and cell death (lactate dehydrogenase) were compared between IL-1-stimulated equine articular cartilage explant cultures and cocultures comprised of osteochondral and synovial explants (OCS). Results suggested that there are differences in responses of culture systems to inflammatory stimulation. In particular, the IL-1-induced fold changes in MMP-13 concentration were significantly different between OCS and cartilage explant culture systems after 96 h. These differences may be relevant to responses of joints to inflammation in vivo and could be important to the biological relevance of in vitro research findings.

Keywords: articular coculture; bone alkaline phosphatase; horse; matrix metalloproteinase-13; osteoarthritis; prostaglandin E2; tumor necrosis factor-alpha.

Figure 1

Mean ± SE concentrations of PGE₂ in media samples of cultures containing osteochondral and synovial explants (OCS) or cartilage explants alone (Cart) that were unstimulated (Neg) or stimulated with IL-1 (10 ng/mL; +) at 48 and 96 h after initiation of treatments. *Within a culture type and time, concentration for IL-1-stimulated culture is significantly different from than that for the unstimulated culture.

Figure 2

Mean ± SE concentrations of tumor necrosis factor-alpha (TNF-alpha) in media samples of cultures containing osteochondral and synovial explants (OCS) or cartilage explants alone (Cart) that were unstimulated (Neg) or stimulated with IL-1 (10 ng/mL; +) at 48 and 96 h after initiation of treatments. ^#Within a time, the fold increase in TNF-alpha concentration between unstimulated and stimulated cultures is significantly different between culture types.

Figure 3

Mean ± SE concentrations of matrix metalloproteinase-13 (MMP-13) in media samples of cultures containing osteochondral and synovial explants (OCS) or cartilage explants alone (Cart) that were unstimulated (Neg) or stimulated with IL-1 (10 ng/mL; +) at 48 and 96 h after initiation of treatments.

Figure 4

Mean ± SE concentrations of dimethyl-methylene blue (DMMB) in media samples of cultures containing osteochondral and synovial explants (OCS) or cartilage explants alone (Cart) that were unstimulated (Neg) or stimulated with IL-1 (10 ng/mL; +) at 48 and 96 h after initiation of treatments.

Figure 5

Mean ± SE concentrations of bone alkaline phosphatase (BAP) in media samples of cultures containing osteochondral and synovial explants (OCS) or cartilage explants alone (Cart) that were unstimulated (Neg) or stimulated with IL-1 (10 ng/mL; +) at 48 and 96 h after initiation of treatments.

Figure 6

Mean ± SE concentrations of lactate dehydrogenase (LDH) in media samples of cultures containing osteochondral and synovial explants (OCS) or cartilage explants alone (Cart) that were unstimulated (Neg) or stimulated with IL-1 (10 ng/mL; +) at 48 and 96 h after initiation of treatments.