J.A. Yu-Yahiro, C.B. Ruff, B.G. Parks, V.S. Sinkov, I. Merchenthaler
Background: To investigate the effect of S-equol, a selective estrogen receptor ß agonist produced in certain individuals by biotransformation of the soy isoflavone daidzein, on bone structure, bone strength, and metabolism in overiectomized rats. Design: Controlled animal study. Participants: Total of 75 female rats. Intervention: Animals were divided into 5 groups: ovariectomized (OVX), OVX+17-beta estradiol benzoate (EB), OVX+S-equol (30 mg/kg), OVX+S-equol (100 mg/kg), and SHAM. Animals received drug or vehicle for 60 days. At sacrifice, right femora and vertebrae (L3 and L4) were excised. Measurements: Bone density and structural parameters were measured by pQCT. Mechanical testing and quantitative histomorphometry were done. Blood markers of bone metabolism and uterine weights were measured. Results: Higher dose S-equol preserved mechanical strength of bone. Vertebral compressive strength, femoral bending strength, and femoral cortical thickness were not different between the S- equol (100 mg/kg) , SHAM, and EB groups and all were significantly higher than OVX and S-equol (30 mg/kg) groups. No differences were found in osteoclast numbers or vertebral bone mineral composition, and serum markers of bone metabolism did not follow the pattern of strength measures differences. Uterine weight in the higher dose S-equol group was significantly lower than in SHAM and EB groups. Conclusions: Treatment of OVX rats with S-equol (100 mg/kg) resulted in preservation of vertebral and femoral bone strength and volume not different from that in SHAM or EB rats. Higher dose S-equol caused less uterine stimulation than did endogenous or synthetic estrogen. These results suggest that S-equol warrants further study as a possible alternative to estrogen replacement for treatment of osteoporosis.