Role of soy protein with normal or reduced isoflavone content in reversing bone loss induced by ovarian hormone deficiency in rats

Abstract

Soy protein, a rich source of isoflavones, fed immediately after an ovariectomy prevents bone loss in rats. Reports of the effectiveness of natural and synthetic isoflavones in preventing or treating osteoporosis led us to examine the effect of soy protein in reversing established bone loss. Seventy-two 95-d-old female Sprague-Dawley rats were assigned to 6 groups. The rats were either sham operated (SHAM; 2 groups) or ovariectomized (OVX; 4 groups) and then fed a casein-based, semipurified diet. Thirty-five days after surgery, 1 SHAM and 1 OVX group were killed to examine the occurrence of bone loss. Thereafter, the other SHAM and 1 OVX groups continued to receive the casein-based diet. Whereas the remaining 2 OVX groups received diets in which casein was replaced by soy protein with normal (OVX+SOY) or reduced (OVX+SOY-) isoflavone content for 65 days. The OVX control group had significantly lower femoral and fourth lumbar vertebral bone densities than the SHAM group. Femoral density of rats fed SOY or SOY- diets were not significantly different from SHAM or OVX controls. This suggests a slight reversal of cortical bone loss that may be partially due to higher femoral insulin-like growth factor I mRNA transcripts resulting from both the SOY and SOY- diets. The ovariectomy-induced increases in indexes of bone turnover were not ameliorated by either of the soy diets, suggesting that any positive effect of soy was achieved through enhanced bone formation rather than slowed bone resorption. Long-term consumption of soy or its isoflavones may be needed to produce small but continued increments in bone mass.

Evaluation of the Preventive Effect of Isoflavone Extract on Bone Loss in Ovariectomized Rats

“…Treatment with isoflavone extract at 6.25 g/kg appeared to prevent bone loss in the femur and lumbar vertebra. These results are supported by previous observations of the positive effects of soybean products -such as soybean protein and soy milk powder -on the bone density of female rats, 8,12,13) because these products contained genistein and daidzein. But, the effects of isoflavone on ALP and TRAP activities are not the same as that of estrogen.…”

“…[5][6][7] Thus it is necessary to develop naturally occurring compounds or synthetic substances with less undesirable side effects that can substitute or reduce the need for drugs used currently. 8,9) Epidemiological studies suggest that the low incidence of osteoporosis and heart disease in postmenopausal Asian women compared to American women is attributable to their higher intake of soybean-based foods. 1,10) Kalu et al 11) observed that feeding soy protein instead of casein to elderly rats prevented agerelated bone loss.…”

“…Soy isoflavones, which have both weak estrogenic and antiestrogenic effects, are structurally similar to tamoxifen, an agent that acts similarly to estrogen in reducing postmenopausal bone loss. 8,12,13) The biological effects of genistein and daidzein have not been fully clarified. Daidzein has been shown to have a y To whom correspondence should be addressed.…”

“…8,23) Moreover, the ovariectomized rat model is suitable for studying problems that are related to postmenopausal bone loss, since this model has been shown to be useful for investigating the cellular mechanisms underlying the action of estrogen on the skeleton. 24) Therefore, the present study was designed to investigate the effect of isoflavone, which was extracted from soybean hypocotyls, on the bone of ovariectomized rats.…”

Role of Soy Diet and L‐Arginine in Cyclosporin‐A‐Induced Osteopenia in Rats

“…Also oestrogenlike substances, such as isoflavone, which are found in some plants such as soy, may have beneficial effects on bone, because they significantly improve the vertebral bone density Author for correspondence: Giuseppe Clementi, Institute of Pharmacology, School of Medicine, University of Catania, Viale A. Doria 6, 95125 Catania, Italy (fax π39 095 7384225, e-mail mangano /tin.it). (Arjmandi et al 1998a). Several studies indicate that soy may have protective effects on bone and it has been suggested that this positive effect is due to isoflavones in the soy content (Arjmandi et al 1998b).…”