Abstract:

BACKGROUND: Long-term use of dexamethasone as a glucocorticoid will destroy the dynamic balance of osteogenesis and osteoclastation, reduce bone mineral density, damage bone biomechanics. A regulation of receptor activator of nuclear factor-κB ligand (RANKL)/osteoprotegerin (OPG) protein pathway may be an approach to improve bone mineral density and bone biomechanics in dexamethasone-induced osteoporosis rats.

OBJECTIVE: To investigate the effects of psoralen corylifolia extract on bone mineral density and bone biomechanics in dexamethasone-induced osteoporosis rats based on RANKL/OPG pathway.

METHODS: Osteoporosis models were established in Wistar rats, SPF grade, using intramuscular injection of dexamethasone. Lentiviral vectors containing OPG gene interference fragments at concentration of 1×10⁷ TU/mL were selected for subsequent experiments. The model rats were randomly divided into model group, no-load group (lentivirus empty vector), OPG silencing group (lentivirus vector containing OPG gene interference fragment), psoralen corylifolia extract group, psoralen corylifolia extract+OPG silencing group, with 12 rats in each group. Another 12 rats were selected as the control group. After drug treatment, bone mineral density of the left femur in rats was measured by bone densitometer; the elastic modulus, maximum load and yield load of the right femur of rats were measured by mechanical testing machine; the mineral salt content in the femur of rats was determined; the levels of RANKL and OPG in the serum of rats were detected by ELISA kit; and the expression levels of RANKL and OPG in bone tissues of rats were detected by western blot. The study protocol was approved by the Animal Ethics Committee of Qinghai University Medical School with an approval No. 2017081501.

RESULTS AND CONCLUSION: (1) Bone mineral density, modulus of elasticity, maximum load, yield load, bone mineral salt content, serum OPG level and OPG protein expression in bone tissues were measured, which were lower in the model group than the control group, lower in the OPG silencing group than the model group, higher in the psoralea corylifolia extract group than the model group, and higher in the psoralen corylifolia extract+OPG silencing group than the OPG silencing group, but lower than the psoralea corylifolia extract group (all P < 0.05). (2) The level of RANKL in serum and the expression of RANKL in bone tissue were measured, which were higher in the model group than the control group, higher in the OPG silencing group than the model group, lower in the psoralea corylifolia extract group than the model group, and lower in the psoralen corylifolia extract+OPG silencing group than the OPG silencing group, but higher than the psoralea corylifolia extract group (all P < 0.05). (3) There was no significant difference in each index between model group and no-load group (P > 0.05). (4) All these findings indicate that psoralea corylifolia extract can increase bone mineral density and improve bone biomechanics in dexamethasone-induced osteoporosis rats, possibly by up-regulating the expression of OPG and down-regulating the expression of RANKL.

Key words: RANKL/OPG pathway, psoralen corylifolia extract, dexamethasone, osteoporosis, RANKL, RANK