Ursolic Acid Prevents Retinoic Acid-Induced Bone Loss in Rats

Objective: To examine the effects of ursolic acid(UA) on mitigating retinoic acid(RA)-induced osteoporosis in rats. Methods: Fifty female Sprague-Dawley rats were randomly divided into the control group(n=10) and the osteoporosis group(n=40). The 40 osteoporosis rats were induced by 75 mg/(kg·d) RA once daily for 2 weeks, and then were randomly assigned to vehicle control(model), low-, middle-, and high-dose UA [(UA-L, UA-M, UA-H; 30, 60, 120 mg/(kg·d), respectively] groups(10 rats each). UA were administered once daily to the rats from the 3 rd weeks for up to 4 weeks by gavage. Bone turnover markers [serum alkaline phosphatase(ALP), osteocalcin(OCN), urine deoxypyridinoline(DPD)] and other parameters, including serum calcium(S-Ca), serum phosphorus(S-P), urine calcium(U-Ca), urine phosphorus(U-P), and bone mineral density(BMD) of the femur, 4 th lumbar vertebra and tibia, bone biomechanical properties and trabecular microarchitecture, were measured. Results: The osteoporosis in rats was successfully induced by RA. Compared with the model group, UA-M and UA-H significantly reversed the RA-induced changes in S-P, U-Ca, U-P, ALP, OCN and urine DPD ratio and markedly enhanced the BMD of right femur, 4 th lumbar vertebra and tibia(P<0.05 or P<0.01). Further, biomechanical test and microcomputed tomography evaluation also showed that UA-H drastically improved biomechanical properties and trabecular microarchitecture(P<0.05 or P<0.01). Conclusion: UA could promote bone formation, increase osteoblastic activity and reduce osteoclastic activity in rats, indicating that UA might be a potential therapeutic of RA-induced acute osteoporosis.