Effect Of Ursolic Acid On Osteoporosis Induced By Oxidative Stress

Osteoporosis（OP）is a kind of metabolic bone disease,which is characterized by damage to the microstructure of bone tissue,decreased bone mass,and easy to cause fractures.Ursolic acid is a kind of triterpenoid compound,which widely exists in Ligustri lucidum and other natural plants.It has good antioxidant effect,few toxic side effects and other advantages,and has a very broad application prospect.The aim of this study is to elucidate the protective effect and mechanism of ursolic acid on osteoporosis under oxidative stress by studying the effects of ursolic acid on oxidative stress-related osteoporosis models in vitro and in vivo.Methods:Thirteen weeks old female Kunming mice（n=7/group）were selected to establish the in vivo model by subcutaneous injection of D-galactose（10 g/kg/d）combined with low calcium diet（0.1%calcium concentration）.At the same time,low,medium and high concentrations of ursolic acid were given by gavage（20mg/kg/d,40mg/kg/d,80mg/kg/d）,and the body weight and food intake of mice were recorded during the experiment.Organ coefficient,malondialdehyde（MDA）content in liver and kidney,superoxide dismutase（SOD）activity,bone coefficient,bone dry/wet ratio,biochemical parameters,calcium balance,bone mineral density（BMD）and other bone morphological parameters were measured 20 days after injection.In vitro,MC3T3-E1cells were treated with H₂O₂to simulate oxidative stress environment for membrane formation.The experimental groups were treated with different concentrations of ursolic acid for 24 h and 48 h.The cell viability,alkaline phosphatase（ALP）level,OPG and RANKL protein secretion levels were measured.At the same time,three MAPK pathway inhibitors PD98059,SB203580 and SP600125 were selected to study the protective effect of ursolic acid on osteoblasts under oxidative stress.Test results:The results in vivo showed that uronate treatment reduced MDA content and increased SOD activity in liver and kidney,decreased urinary calcium creatinine value,decreased calcium loss,increased bone coefficient and bone dry/wet ratio,increased BMD,BV/TV,Tb.N and Tb.Th,and decreased BS/BV,Tb.Histological observation showed that the loss of trabecular bone was reduced,and the integrity of bone microstructure was increased,and the medium and high concentrations had the best effect.The results of in vitro experiments showed that ursolic acid at the concentration of 50-20μm had the best protective effect on osteoblasts.Ursolic acid at the concentration of 50-10μm could increase the secretion level of OPG protein and increase the OPG/RANKL ratio.Signal pathway test showed that the protective effect of ursolic acid on H₂O₂oxidative damage of osteoblasts was related to three MAPK pathways,including p38MAPK,JNK and ERK.Conclusion:Ursolic acid can inhibit oxidative stress damage,improve calcium loss,increase bone mineral density and trabecular bone,improve bone microstructure,and reduce the level of free radicals in the body.In vitro,it can promote the proliferation of osteoblasts through p38MAPK,JNK and ERK pathways,increase cell activity and OPG protein secretion,and up-regulate the OPG/RANKL ratio,thereby protecting osteoblasts from oxidative stress.