Aucubin Improves Osteoporosis Via Inhibition On Osteoclast Differentiation Related To Nrf2-mediated Antioxidation

Osteoporosis(OP)is considered to be a chronic osteopathy that has long been perplexing many elderly patients.With the increasing number of glucocorticoid induced osteoporosis(GIOP),GIOP has attracted the attention of many researchers.We also proved that the occurrence of GIOP is closely related to oxidative stress,and oxidative stress is characterized by the excessive production of reactive oxygen species(ROS).It can inhibit the differentiation of osteoblasts,enhance the differentiation of osteoclasts,accelerate the over absorption of bone,and further lead to OP,so it plays a very important role in the occurrence and development of OP.Although there are some anti OP drugs on the market,the adverse reactions and side effects they show are not very suitable for the group with special history and drug tolerance and the therapeutic effect is not significant,so we choose to extract effective ingredients from natural,non-toxic and reliable natural Chinese herbal medicines for pharmacological activity research.Aucubin(AU)is a natural monomer extracted from Eucommia ulmoides,a famous Chinese herbal medicine.We have proved that aucubin has a very significant effect on bone protection and OP improvement by pharmacological experiments.In this study,nuclear factors were first adopted-κ Receptor activator of nuclear factor-κ B ligand(RANKL)induced RAW264.7 cells into osteoclasts,and observed the inhibition of AU on its over differentiation after administration of AU.Then,the OP mice model was established by injection of dexamethasone(DEX)into C57BL/6mice.The model can simulate the pathological condition of patients with glucocorticoid osteoporosis.The results further verified the bone protection effect of AU on OP mice.According to the existing research results,the dosage of AU reduces the number of tartrate resist acid phosphatase(TRAP)positive cells in osteoclasts.The results showed that the expression of TRAP,NFATc1,CTSK was significantly increased by AU administration.The expression of collagen type I(COL-I)can be seen from Western blot experiment results.It can be seen that the dosage of AU can increase the expression level of nuclear factor erythrid 2 related factor 2(Nrf2),and affect the downstream protein and catalase(CAT)related to oxidative stress.The expression level of heme oxygenase-1(HO-2),superoxide dismutase-1(SOD-1),superoxide dismutase-2(SOD-2)was improved,and the physiological and skeletal state of OP mice were improved.It was proved that the therapeutic effect of AU on OP was related to Nrf2 mediated antioxidant effect.AU has been shown in previous studies to regulate OP by promoting the formation of osteoblasts.In this study,after DEX injection and establishment of OP mouse model,the cortical bone wall of femur and tibia of OP mice became thinner,bone mineral density(BMD)decreased,chondrocytes decreased,bone mass and bone strength decreased.After 7 weeks of administration,AU could reduce pathological changes,increase the number of trabeculae and reduce the loss of chondrocytes,BMD,bone surface area/bone volume(BS/BV),bone volume/tissue volume(BV/TV),trabecular thickness(Tb.Th),trabecular number(Tb.N)were increased,and the trabecular spacing(Tb.Sp)content was reduced,AU also reduced the level of tartrate resist acid phosphatase 5b(TRAP5b),C-terminal terminal peptide of type I collagen(CTX-1).The content of N-terminal protein of type I procollagen(PINP),recombinant bone morphogenetic protein-2(BMP-2),bone morphogenetic protein receptor-2(BMPR-2)and type I collagen(COL-I)were increased.Moreover,AU also effectively inhibited the overexpression of ROS,IL-1 induced by DEX,and increased the content of SOD and CAT.In conclusion,it is proved that AU can effectively inhibit the formation of osteoclasts to prevent and treat OP,and improve OP by up regulating Nrf2 signaling pathway and its downstream protein expression.Meanwhile,in OP mice induced by DEX,it also has inhibitory effect on osteoclast differentiation in mice and can improve the abnormal physiological condition and bone adverse physiological changes caused by OP.The excellent medicinal value of AU in OP can be a potential substitute for estrogen and diphosphate,and provide a strong experimental basis for the development of AU drugs in OP in the future.