Adverse changes in cortical and trabecular bone compartments of the femur in rats with adjuvant-induced arthritis after one remodelling cycle

Abstract

It is widely known that rheumatoid arthritis (RA) is associated with articular bone damage. However, there is still not enough information on whether the inflammatory process can deteriorate bone microstructure outside the joint as well. Furthermore, the impact of RA on the microscopic structure of cortical and trabecular bone, including parameters of bone microarchitecture, strength, and geometry after one remodelling cycle, has not been determined, yet. Therefore, this study investigated possible alterations in both cortical and trabecular bone compartments of the femur in a rat model of adjuvant-induced arthritis (AA) 28 days post disease induction. AA was generally evoked by a single intradermal injection ofsuspension of heat-inactivated Mycobacterium butyricumin incomplete Freund’s adjuvant. We have found that AA resulted in inflammation as evidenced by increased hind paw swelling, decreased levels of circulating albumin, and elevated levels of nitrite/nitrate, interleukin-1β. Detrimental changes in examined bone parameters related to microarchitecture, strength, and geometry were revealed in AA rats. Overall, AA was associated with bone loss, decreased bone mineral density in bothcortical and trabecular bone compartments, as well as reduced mechanical competence, and more intense vascularization in the cortical bone. According to our results, AA-related inflammation caused structural degradation of cortical and trabecular bone quality, as well as mechanical weakness in the femoral diaphysis leading to bone fragility after only one remodelling cycle. The findings focused on the femoral diaphysis, which is located outside the joint, are the first in this field of research