ZA had a slight pro-inflammatory effect, whether used alone or in combination with MTX.(b)Body weight (g) measured at each clinical evaluation. mass density was evaluated by densitometry. == Results == MTX significantly decreased the severity of CIA, whereas ZA slightly exacerbated it. When these two drugs were used in combination, MTX prevented the pro-inflammatory effect of ZA. The combination of ZA with MTX was more effective than MTX alone for reducing structural joint damage with a dramatic decrease of osteoclasts’ number in the eroded joints. However, MTX alone FLAG tag Peptide also significantly FLAG tag Peptide reduced the number of osteoclasts and the number of CD68+ mononuclear cells. ZA alone, or ZA with MTX, significantly increased the systemic bone mass density measured by densitometry and bone volume on histomorphometric analysis. == Conclusions == A combination of MTX and ZA prevented both bone erosion and systemic bone loss in a rat model of arthritis. Both treatments independently decreased the number of osteoclasts in the eroded joint. However, while MTX probably acts mainly through a decrease of inflammation, ZA has a direct effect on osteoclasts, allowing a dramatic down-regulation of these cells in inflamed joints. These two different mechanisms of action provide support for the use of a combination of these two drugs to improve the prevention of structural joint damage in RA. == Introduction == Rheumatoid arthritis (RA) is characterized by a chronic inflammation of synovium, leading to progressive joint destruction. Erosions of the periarticular bone, the most specific hallmark of the disease, produce deformation, laxity, and functional disability. Local and systemic inflammation SCA12 also favors generalized osteopenia or osteoporosis. Osteoclasts are considered as the principal cell type responsible for focal bone resorption in RA [1,2]. Gravallese and colleagues first described tartrate resistant acid phosphatase (TRAP) positive multinucleated cells in resorption lacunae at the bone-pannus interface in patients with juvenile arthritis [3]. Several lines of evidence have since confirmed the role of osteoclasts in bone destruction during RA. Osteopetrotic mouse models with FLAG tag Peptide a genetic block in osteoclast formation, such as receptor activator of nuclear factor kappa B-ligand (RANK-L) -/- mice, develop arthritis but display no bone erosion [4]. Treatment with a chimeric osteoprotegerin fusion protein, which inhibits osteoclast differentiation, efficiently prevents bone erosion in the rat FLAG tag Peptide collagen-induced arthritis model [5]. The origin of osteoclasts in arthritic joints remains unclear. These cells may differentiate from monocytic precursor cells that home to the inflamed synovial tissue or from bone marrow precursors, under the influence of cytokines, such as RANK-L or TNF-alpha, generated in the synovium of patients with RA [6]. Transdifferentiation from other subsets of immune cells, including dendritic cells, has also been proposed [7]. Osteoporosis in RA patients may be attributed to various risk factors, including primary osteoporosis risk factors, immobilization, use of corticosteroids, and systemic inflammation. Osteoclasts also play a crucial role in the development of generalized osteoporosis, mediated through the osteoprotegerin/RANK/RANK-L signaling system [8]. Recent studies have demonstrated that targeting RANK-mediated osteoclastogenesis with denosumab prevents systemic bone loss in RA patients [9]. The prevention of joint damage and systemic bone mass loss is a key goal of treatment for RA. Zoledronic acid (ZA), a nitrogen-containing third-generation bisphosphonate, is widely used to treat metastatic bone disease and has recently been used for osteoporosis [10,11]. ZA, like other bisphosphonates, has a direct effect on mature osteoclasts, inducing their apoptosis and inhibiting their activity. ZA has been shown to be effective for the prevention of osteoporosis, but its ability to confer local joint protection remains a matter.