OBJECTIVETo observe the effect of a slow-release recombinant human bone morphogenetic protein-2 (rhBMP-2) formulation on the expressions of receptor activator of nuclear factor-κB ligand (RANKL) and osteoprotegerin (OPG) in a murine air pouch model of bone implantation.

METHODSA cranial bone allograft was implanted in the air pouch induced on the back of the recipients. The rat models were then randomized into 5 groups, including a blank control group, chromium particle group, and 3 rhBMP-2 groups receiving 50, 100 or 200 µg/L slow-release rhBMP-2 in addition to chromium particles. Three weeks later, the expressions of RANKL and OPG in the air pouch was detected using Western blotting and RT-PCR, and the positively stained area for osteoclasts in the bone graft was determined with TRAP staining for drug effect assessment.

RESULTSRANKL and OPG expressions were found in the air pouches in all the 5 groups. RANKL and OPG protein and mRNA expressions, RANKL/OPG ratio and osteoclast staining area in the bone graft were the highest in chromium particle group (P<0.05), but were significantly decreased by treatment with the slow-release rhBMP-2 formulation (P<0.05); the measurements showed no significant differences between the blank control group and 200 µg/L rhBMP-2 group (P>0.05).

CONCLUSIONChromium particles can cause osteolysis by increasing the RANKL/OPG ratio in rats, and intervention with slow-release rhBMP-2 can significantly promote bone formation and suppress bone resorption by decreasing RANKL/OPG ratio.