Evaluation of Cartilage and Bone Degradation in a Murine Collagen Antibody-induced Arthritis Model (1)
Rheumatoid arthritis (RA) is characterized by expression of autoantibodies, upregulation of cytokines, and involvement of major histocompatibility complex (MHC) class II genes. Collagen‐induced arthritis (CIA) has proven to be one of the favourable models of RA. Collagen antibody‐ and lipopolysaccharide‐induced arthritis (CAIA‐LPS) triggered by antibody binding bypasses immune activation and thus, this model can be established in a variety of mouse strains such as CIA‐resistant, T‐cell deficient, knockout, and transgenic mice. Microscopic assessment of a joint status is still a gold standard in animal studies, however, the advance in biotechnology raises the development of new techniques and methods such as for example microcomputer tomography (micro‐CT), which gives a possibility for further characterization of presented animal models.
Whereas 100% of Balb/c mice displayed a homogenous onset of disease from day 6, which remained throughout the study period. The severity of disease increased progressively up to termination of the experiment, and on day 15, the mean total paw inflammation score for each of the four CAIA‐LPS Balb/c groups had reached a similar level (11–14) that was significantly different from the non‐diseased control group. However only 75% of the CD‐1 mice (24 of 32 animals) showed evidence of disease on day 6, and this number decreased progressively to 25% (8 of 32 animals) on the day of the termination for these mice (day 12).
The cartilage destruction was extensive and typified by proteoglycan loss and cartilage erosion/ulceration. The bone resorption was characterized by juxtra‐articular/subchondral bone loss with osteoclasts infiltration while osteophyte formation was characterized by periosteal bone proliferation. The periosteal bone proliferation and bone resorption corroborated the micro‐CT changes. Serum CTX‐II levels were approximately 43–64% higher in untreated diseased animals compared with non‐diseased controls. Dexamethasone Balb/c group had a mean total paw inflammation score of 3.4 at study termination, which was significantly different from the corresponding CAIA‐LPS group. The same tendency was noted microscopically. However, minimal to moderate cartilage degeneration, typified by proteoglycon loss was observed in mice of the dexamethasone treated group accounting for the incomplete but still statistically significant inhibition of the mean histological score in the dexamethasone group compared with group 3. Treatment with dexamethasone resulted in significantly lower serum CTX‐II levels.
Qualitative evaluation of 3‐D micro‐CT scans of the first tarsal bone revealed the presence of new periosteal bone formation (osteophytes). Osteophyte formation was increased approximately two‐fold in CAIA‐LPS Balb/c animals compared with non‐diseased controls, although differences failed to attain statistical significance. Bone Mineral Density (BMD) in CAIA‐LPS Balb/c mice was slightly, although significantly lower compared with the non‐diseased group.
The bone architecture in the tarsal joint of normal mice showed no destruction as evidenced by the presence of a smooth bone surface. In contrast, CAIA‐LPS mice exhibited substantial bone destruction. The administration of dexamethasone protected bone that resulted in a close to normal bone microarchitecture
Micro‐CT has proven to be a powerful technique to analyse bone structure and density in different animal models. The study using the CAIA‐LPS model demonstrated decreased BMD and elevation of bone turnover in diseased animals. CTX‐II can predict the future cartilage damage. In addition to that, immunohistochemistry carried out in all these models have demonstrated the co‐localization of CTX‐II and damaged cartilage.