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Background: Clinically oriented and easy to handle animal models are urgently needed to test pharmacologic treatment of cartilage trauma to reduce the resulting tissue damage by chondrocyte apoptosis and induction of matrix-degrading enzymes. Aim: To develop a biomechanically defined cartilage trauma model. Material and Methods: We constructed a novel trauma device that allows biomechanically defined force application to the load-bearing region of the medial and lateral femoral condyles in adult rabbits. The fixation to the femur was specially designed to avoid uncontrolled influx of blood into the joint. The device was tested on the articular femoral surface of cadaveric rabbits. Results: At a lower energy (1.0 J), the tests showed that superficial and partially deep fissuring, partial necrosis of the chondrocytes, and early proteoglycan loss occurred at the region of impact. Subchondral fractures could be excluded by micro CT. At higher energy (≥1.4 J), we observed more pronounced deep fissuring and in some cases complete shearing of the articular cartilage from the subchondral bone. Conclusion: Our model represents an easy to use method to create a biomechanically defined cartilage trauma and offers some advantages with respect to handling under aseptic surgical conditions and prevention of uncontrolled intra-articular bleeding from the bone marrow compartment for pharmacologic studies. [ABSTRACT FROM AUTHOR]

Injury to articular cartilage is often associated with an inflammatory reaction and frequently results in the development of post-traumatic osteoarthritis (post-traumatic OA). Cell death, inflammation and loss of proteoglycans participate in these mechanisms with p38MAPK being one of the pivotal signaling kinases. Therefore, the interaction of trauma and of the pro-inflammatory cytokine IL-1β was investigated in an in vitro tissue model of human osteoarthritic cartilage. Trauma was induced by impacting cartilage explants with a drop-tower system and its effect was measured in terms of cell survival, gene expression and the release of mediators. In addition, the effect of concomitant IL‑1β stimulation and p38MAPK inhibition by SB203580 was investigated. We found a significant decrease in chondrocyte viability after trauma, but no additional effect of IL-1β stimulation. SB203580 had a tendency to improve cell survival suggesting a role for p38 signaling in cell viability after impact in an inflammatory environment. We showed that various mediators are released in response to trauma with or without IL-1β stimulation, differing in composition and time response. Trauma resulted in an increased release of IL-6, whereas TNF-α and IL-1β release was unaffected. Prostaglandin (PG) and NO synthesis pathways were both affected by trauma and/or IL-1β. We demonstrate for the first time an elevated release of prostaglandin D2 (PGD2) by human articular cartilage in response to a single mechanical impact. The up-regulation of mediators was time-dependent, with a more early increase of PGD2 compared to prostaglandin E2 (PGE2) and a late induction of NO by co-stimulation with IL-1β between 6 and 24 h.

Articular chondrocytes respond to extracellular influences by activating signaling pathways which change gene expression. One key signal transduction pathway of inflammatory joint disease is mediated by the p38MAPK which is known to be activated by the pro-inflammatory cytokine IL-1beta. We used the p38MAPK inhibitor SB203580 and a whole human genome microarray in an in vitro inflammation model to identify genes regulated by this pathway in human chondrocytes. We found that 1,141 genes were regulated by IL-1beta, and 646 genes were regulated by the inhibitor whereas 116 genes were co-regulated by both substances. To elucidate the overall effect of SB203580, a GoMiner pathway analysis was performed which revealed involvement of versatile biological processes. Predominantly affected terms were 'response to stimulus', 'oxygen metabolism' and 'ligase activity'. We discuss herein the relevance and function of affected fields including the involved genes and unexpected effects of p38MAPK inhibition as it relates to the context of cartilage. Our results do not predict a pro-apoptotic or cancer promoting effect and markedly extend the knowledge on p38MAPK inhibition in chondrocytes beyond primary target genes.