Daidzein is more efficient than genistein in preventing ovariectomy-induced bone loss in rats

We investigated the ability of genistein and daidzein, two soybean isoflavo nes, compared with that of 17 alpha-ethinylestradiol, to prevent bone loss in ovariectomized rats, a model for postmenopausal osteoporosis. Female Wis tar rats (n = 65; 12 mo old) were either sham-operated (SH; n = 13) or ovar iectomized (OVX; n = 52). On d 0, OVX rats were randomly assigned to groups as follows: 13 received genistein [G; 10 mu g/g body weight . d)], 13 were treated with daidzein [D; 10 mu g/g body weight . d)], 13 received 17 alph a-ethinylestradiol [E-2; 30 mu g/kg body weight . d)] and 13 were untreated (OVX). Compounds were mixed with a soy protein-free powdered semipurified diet and given orally for 3 mo. On d 90, the bone mineral density (BMD) in lumbar vertebrae, femur and its metaphyseal and diaphyseal zones (rich in c ancellous and cortical bone, respectively) was lower in OVX than in SH (P < 0.01). In D or E-2, the four BMD were not different from SH, whereas in G, only the diaphyseal BMD was not different from SH. Image analysis performe d in the distal femur metaphysis revealed that the cancellous bone area was lower in OVX than in SH (P < 0.01). Only the area in D was not different f rom that in SH. Finally, the bone turnover, which was higher in OVX than in SH (P < 0.005 and P < 0.05 for plasma osteocalcin concentration and urinar y deoxypyridinoline excretion, respectively), was not different in G, D or E-2 compared with SH. Therefore, consumption of 17 alpha-ethinylestradiol o r daidzein was more efficient than genistein in preventing ovariectomy-indu ced bone loss in rats.