Ipriflavone inhibits bone resorption in intact and ovariectomized rats

Abstract

Abstract. The aim of this study was to investigate the possible inhibitory effect of ipriflavone on bone resorption in rats. For this purpose, 10-week-old, intact and ovariectomized (OVX) rats, prelabeled from birth with [3 H]-tetracycline, were used. Bone resorption was monitored by measuring the urinary excretion of [ 3 H]. The animals were fed a purified diet devoid of naturally occurring flavonoids. In the intact rats, the daily meal was given either as a single portion or divided into four portions, a procedure known to lead by itself to a decrease in bone resorption. Ipriflavone, given 7 days after OVX at the dose of 400 mg/kg B.W. daily mixed with the food, led within 2-3 days to a significant decrease in bone resorption equivalent to that of 27.2 p g/kg S.C. of 1713-estradiol. The inhibition was sustained for the length of the experiment, up to 21 days. Ipriflavone given 7 days before OVX prevented the increase in bone resorption induced by castration, the effect being dose-dependent between 50 and 400 mg/kg B.W. In contrast to 1713-estradiol, a 5-week treatment with ipriflavone failed to prevent the OVX-induced uterine atrophy. Significant inhibition of bone resorption was also seen in intact animals, provided they rapidly ingested the daily meal. Actually, the decrease in bone resorption induced by portioning the daily food masked the inhibitory effect of ipriflavone in intact animals. In conclusion, ipriflavone can decrease bone resorption in both intact and OVX animals given a purified diet as a single daily meal. In the OVX model, ipriflavone mimics the osteoprotective effect of estrogen. However, the lack of a uterotropic effect suggests that the compound can discriminate between bone and reproductive tissues.Key words: Ipriflavone -Bone resorption -Ovariectomized rats.Ipriflavone is a synthetic derivative of a natural isoflavone. First clinical trials indicate that the compound exerts a beneficial effect in osteopenic diseases [1][2][3]. It is not clear yet whether ipriflavone acts primarily by inhibiting bone resorption or by stimulating bone formation. Inhibition of osteoclast recruitment in both in vitro [4,5] and in vivo [6], and induction of markers of the osteoblast phenotype in vitro [7,8] have been demonstrated. However, in the rat model of osteopenia following ovariectomy [9], ipriflavone did not reduce bone resorption when administered alone, but it did enhance the therapeutic effects of estrogen. Confounding factors may explain the lack of the protective effect of ipriflavone per se on bone loss due to estrogen withdrawal in animals. Therefore, we investigated in vivo the modalities by which an intrinsic inhibitory activity of ipriflavone on bone resorption can be disclosed.For measuring bone resorption, we used a technique based on long-term prelabeling with [ 3 H]-tetracycline and the subsequent determination of urinary excretion of the tracer (Fig. 1). This technique allows monitoring of bone resorption, daily or at shorter intervals, over extended periods of time [10].According to t...

Cross-species and interassay comparisons of phytoestrogen action.

“…These doses produce plasma concentrations (135) similar to the in vitro concentrations (≥ 100 nM) required for inhibition of osteoclast differentiation (136) and bone resorption (137). Much higher oral doses (50-400 mg/kg/day) of IPR have been required to prevent bone loss in ovariectomized rats (138), doses that also produce plasma concentrations similar to the effective in vitro concentrations (139,140). COM also inhibits bone resorption in vitro (141) and is a more potent agent, preventing bone loss at oral doses of 1-2 mg/kg/day (142,143).…”

Quercetin Suppresses Bone Resorption by Inhibiting the Differentiation and Activation of Osteoclasts

“…; rats fed onions increased their bone mass. 8) Onion also inhibits bone resorption stimulated in ovariectomized rat, 9,10) and an extract from onion is known to prevent tibial cortical and cancellous bone loss induced by a combination of low protein intake and diet-mediated mild hyperparathyroidism in rats.…”

“…7) Among them, onions have been shown to have the strongest properties to regulate bone metabolism 7) ; rats fed onions increased their bone mass. 8) Onion also inhibits bone resorption stimulated in ovariectomized rat, 9,10) and an extract from onion is known to prevent tibial cortical and cancellous bone loss induced by a combination of low protein intake and diet-mediated mild hyperparathyroidism in rats. 11) Rutin (quercetin-3-O-glucose rhamnose) ( Fig.…”

The Relationship of Mandibular Bone Density Level to Femur Bone Density Level in Ovariectomized Female Rats given Isoflavones and 17-estradiol

“…Cecchini et al stated that large bone resorption in skeleton reached 40% within the first week after ovariectomy was monitored based on pre-label tetracycline [20]. Associated with the manifestation of estrogen depletion in experimental animal bones, found an increased in IL-1, IL-6, and TNF in osteoblasts stimulate osteoclast synthesis with accelerated bone resorption [21].…”