OBJECTIVETo evaluate the effects of sonicated extracts of Porphyromonas gingivalis (Pg) on receptor activator of NF-κB ligand (RANKL) and osteoprotegerin (OPG) expression in human periodontal ligament cells (HPDLC) and the effect of Pg on bone resorption in periodontitis.

METHODSHPDLC were exposed to 25, 50 mg/L sonicated extracts of Pg for 6 h, HPDLC without treatment served as control. The expression of RANKL-OPG mRNA and protein were examined by real time polymerase chain reaction and Western blotting. OPG protein in the supernatant was examined by enzyme linked immunosorbent assay (ELISA). The data were statistically analyzed by SPSS 13.0 and one-way analysis of variance (ANOVA).

RESULTSWhen HPDLC were exposed to sonicated extracts of Pg, the expression of RANKL mRNA and protein in 25 mg/L and 50 mg/L groups were higher than that of control group (P < 0.05), the expression of OPG mRNA in 50 mg/L group (0.087 ± 0.021) was lower than that of control group (0.240 ± 0.019) (P < 0.05), and OPG protein in 25 mg/L and 50 mg/L groups (0.813 ± 0.007, 0.398 ± 0.009) was lower than that of control group (1.131 ± 0.005) (P < 0.01). OPG protein expression in the supernatant was not significantly different between experimental group and control group.

CONCLUSIONSSonicated extracts of Pg exposed to HPDLC can up-regulate RANKL expression, down-regulate OPG expression and influence bone metabolism.