Ursolic Acid Prevents Retinoic Acid-Induced Bone Loss in Rats

To examine the effects of ursolic acid (UA) on mitigating retinoic acid (RA)-induced osteoporosis in rats.

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 3rd 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, 4th lumbar vertebra and tibia, bone biomechanical properties and trabecular microarchitecture, were measured.

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, 4th lumbar vertebra and tibia (Plt;0.05 or Plt;0.01). Further, biomechanical test and microcomputed tomography evaluation also showed that UA-H drastically improved biomechanical properties and trabecular microarchitecture (Plt;0.05 or Plt;0.01).

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.