Effects of pamidronate disodium on the loss of osteoarthritic subchondral bone and the expression of cartilaginous and subchondral osteoprotegerin and RANKL in rabbits

Background: Osteoarthritis (OA) is a major health problem in the increasingly elderly population. Therefore, it is crucial to prevent and treat OA at an early stage. The present study investigated whether pamidronate disodium (PAM), a bone-loss inhibitor, can significantly prevent or reverse the progression of early anterior cruciate ligament transection (ACLT)-induced OA. Whether therapeutic intervention is associated with regulation of the expression of Osteoprotegerin (OPG), receptor activator of nuclear factor-κB ligand (RANKL), metalloproteinase-9 (MMP-9) or Toll-like receptor-4 (TLR-4) in cartilage and/or subchondral bone was also investigated.

Methods: 60 New Zealand rabbits were randomized into four groups: Sham-operated (n = 20); ACLT (n = 20); short-term treatment with PAM (PAM-S, n = 10) and long-term treatment with PAM (PAM-L, n = 10). For cartilage and subchondral bone testing, rabbits from Sham and ACLT groups were harvested at 2, 4, 6, and 14 weeks. Rabbits were given PAM from the 4th week after ACLT operation in PAM-S and PAM-L group, and were harvested at 6 and 14 weeks, respectively. Trabecular characteristics and cartilage changes were detected using Micro-CT, safranin O and rapid green staining, respectively. Immunohistochemical staining for OPG and RANKL were also performed. OPG, RANKL, MMP-9 and TLR-4 expression was evaluated by western blot analysis.

Results: Micro-CT and histology analyses indicated that PAM treatment for 2 or 10 weeks could completely prevent or reverse osteoarthritic subchondral bone loss and cartilage surface erosion. Immunohistochemistry and western blot analysis indicated that expression of OPG and RANKL increased, although RANKL expression increased more significantly than that of OPG. Therefore the ratio of OPG to RANKL was lower in the ACLT group. However, the ratio of OPG to RANKL in the PAM group was significantly higher than that in the ACLT group. Additionally, expression of MMP-9 and TLR-4 were upregulated in the ACLT group and downregulated in the PAM treated groups.

Conclusions: PAM can significantly inhibit and even reverse early osteoarthritic subchondral bone loss, thus alleviating the process of cartilaginous degeneration. The mechanisms involved may be associated with the upregulation of OPG expression, and downregulation of RANKL, MMP-9 and TLR-4 expression.