Objective:

2

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

Methods:

2

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.

Results:

2

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 (

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:

2

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.