Inhibition of parathyroid hormone-stimulated resorption in cultured fetal rat long bones by the main metabolites of ipriflavone

The Protective and Therapeutic Effect of Exclusive and Combined Treatment with Alpha-ketoglutarate Sodium Salt and Ipriflavone on Bone Loss in Orchidectomized Rats

OBJECTIVE

This study investigated the effect of alpha-ketoglutarate sodium salt (AKG) and ipriflavone (IP) treatment on the mineralization of the tibia in male rats during the development and after the establishment of osteopenia.

DESIGN

One hundred and twenty eight male rats were randomly selected and submitted to either sham-operation (SHO) or orchidectomy (ORX), after which each group were then randomly divided between the two experiments. In Experiment-1, treatment with AKG or/and IP started after a 7-day recovery period, whereas in Experiment-2, the experimental protocol proceeded after a 60-day period of osteopenia establishment. AKG was then administered as an experimental drinking, at a concentration of 1.0 mol/l. As a control, a placebo solution was administered. IP at 50 mg/kg b.w., and physiological saline - PhS (as a control for IP) were applied daily via gavage.

MEASUREMENTS

After 60 days of experimental treatment, in both experiments, the rats were sacrificed, their body weight recorded, while blood serum (Osteocalcin, CTX) and isolated tibia (weight, length, pQCT, DXA, 3-point bending test) were stored for further analysis.

RESULTS AND CONCLUSIONS

Our results show that during the development of osteopenia, AKG and IP when applied exclusively, counteracts osteopenia development, whereas their usage after the establishment of osteopenia, significantly limits the development of bone disorders. Furthermore, combined treatment of AKG and IP exceeded the effects of their sole usage. In addition, during the development of osteopenia, AKG and IP not only inhibited bone resorption, but markedly stimulated the formation of bone tissue. Finally, after the development of osteopenia, combined treatment with AKG and IP protected the bone tissue against orchidectomy-induced bone loss.

Characterization of cytochrome P450s mediating ipriflavone metabolism in human liver microsomes

Ipriflavone, a synthetic flavonoid for the prevention and treatment of osteoporosis, has been reported to be extensively metabolized in man to seven metabolites (M1-M7). This study was performed to characterize the human liver cytochrome P450s (CYP) responsible for the metabolism of ipriflavone. Hydroxylation at the beta-ring to M3, O-dealkylation to M1 and oxidation at isopropyl group to M4 and M5 are major pathways for ipriflavone metabolism in three different human liver microsome preparations. The specific CYPs responsible for ipriflavone oxidation to the active metabolites, M1, M3, M4 and M5 were identified using a combination of correlation analysis, immuno-inhibition, chemical inhibition in human liver microsomes and metabolism by expressed recombinant CYP enzymes. The inhibitory potencies of ipriflavone and its five metabolites, M1-M5 on seven clinically important CYPs were investigated in human liver microsomes. Our results demonstrate that CYP3A4 plays the major role in O-dealkylation of ipriflavone to M1 and CYP1A2 plays a dominant role in the formation of M3, M4 and M5. Ipriflavone and/or its five metabolites were found to inhibit potently the metabolism of CYPs 1A2, 2C8, 2C9 and 2C19 substrates.

Synthesis, pharmacological evaluation, and structure-activity relationships of benzopyran derivatives with potent SERM activity

The synthesis, binding affinity for estrogen receptor subtypes (ER alpha and ER beta) and pharmacological activity on rat uterus of a new class of potent ligands, characterized by a 3-phenylbenzopyran scaffold with a basic side chain in position 4, are reported. Some of these compounds, endowed with very high receptor affinity, showed potent inhibition of agonist-stimulated uterine growth, with no or limited proliferative effect. Binding affinity mostly depended on the nature and position of substituents at the 3-phenyl ring, while the uterine activity seems to be affected by basic chain length. Compound 9c (CHF4227) showed excellent binding affinity and antagonist activity on the uterus. The docking of benzopyran derivatives explained the structure-affinity relationships observed for 3-phenyl substitution: a small, hydrophobic 4'-substituent could interact with a small accessory binding cavity, while di-substitution at 4' and 3' led to some ER alpha selectivity. This selectivity can be ascribed to differences in amino acid composition and side chain conformation in the region accommodating the 3-phenyl ring at human ER alpha and ER beta ligand-binding domain.

Phytoestrogen genistein acts as an estrogen agonist on human osteoblastic cells through estrogen receptors alpha and beta

Genistein, a soybean isoflavone, has estrogen-like activity in mammals, including the prevention of bone loss. However, whether its mechanism of action on bone turnover is distinct from that of estrogen or raloxifene is unknown. Although genistein has been reported to bind both estrogen receptor (ER) isoforms (alpha and beta), little is known concerning differential activation of gene expression via these ER isoforms. To examine this question, comparison of the responses of normal fetal osteoblast (hFOB) cells stably expressing either ERalpha (hFOB/ERalpha9) or ERbeta (hFOB/ERbeta6), to treatment with genistein, 17beta-estradiol (E(2)) or raloxifene were conducted. In hFOB/ERalpha9 cells, both genistein and E(2) increased the endogenous gene expression of the progesterone receptor (PR), the proteoglycan versican, and alkaline phosphatase (AP), but inhibited osteopontin (OP) gene expression and interleukin-6 (IL-6) protein levels. Raloxifene had no effect on these bone markers. Genistein, but not raloxifene, also mimicked E(2) action in the hFOB/ERbeta6 cells increasing PR gene expression and inhibiting IL-6 production. To determine whether the gene regulatory actions of genistein in human osteoblast cells occur at the level of transcription, its action on the transcriptional activity of a PR-A promoter-reporter construct was assessed. Both genistein and E(2) were found to stimulate the PR promoter in the hFOB cell line when transiently co-transfected with either ERalpha or ERbeta. Whereas hFOB cell proliferation was unaffected by E(2), raloxifene or genistein at low concentrations, higher concentrations of genistein, displayed significant inhibition. Together, these findings demonstrate that genistein behaves as a weak E(2) agonist in osteoblasts and can utilize both ERalpha and ERbeta.

Ipriflavone inhibits osteolytic bone metastasis of human breast cancer cells in a nude mouse model

Osteolytic bone metastasis is a frequent problem in the treatment of cancer. Ipriflavone, a synthetic isoflavone that inhibits osteoclastic bone resorption, has been used for the treatment of osteoporosis in some countries. Some other isoflavones also exhibit an antitumor effect in vitro and in vivo. Here, we studied the effects of ipriflavone on osteolytic bone metastasis of MDA-231 human breast cancer cells injected intracardially into athymic nude mice (ICR-nu/nu). Daily oral administration of ipriflavone at 12 mg/mouse significantly inhibited the development of new osteolytic bone metastases (p < 0.05) and the progression of established osteolytic lesions (p = 0.01), prolonging the life of tumor-bearing mice (p = 0.01 vs. control). In addition, ipriflavone reduced the number of osteoclasts at the bone-cancer interface with no severe adverse effects on the host. In vitro, ipriflavone inhibited the proliferation and DNA synthesis of MDA-231 cells and blocked the ligand-induced phosphorylation of Tyr(845) of the EGFR. Ipriflavone did not promote apoptosis of MDA-231 cells. Our results show that ipriflavone not only directly inhibits the growth of cancer cells but also reduces osteoclasts to prevent the soft tissue tumor burden and osteolytic bone metastases. These findings raise the possibility that ipriflavone may be of use as a therapeutic agent against osteolytic bone metastasis.

Flavonoids: old and new aspects of a class of natural therapeutic drugs

Flavonoids are natural products widely distributed in the vegetable kingdom and currently consumed in large amounts in the daily diet. Flavonoids are capable of modulating the activity of enzymes and affect the behaviour of many cell systems, suggesting that the compounds may possess significant antihepatotoxic, antiallergic, anti-inflammatory, antiosteoporotic and even antitumor activities. This review summarizes available data on these beneficial effects of flavonoids.