Protective effect of plant extract from Onobrychis ebenoides on ovariectomy-induced bone loss in rats
Introduction
Hormone replacement therapy, after 25 years of application, was the treatment of choice for the prevention and therapy of postmenopausal osteoporosis. The beneficial effect of estrogens on bone mass and fracture incidence has been reported by several investigators [1], [2]. However, the recent publication by the Women's Health Initiative has raised serious concerns about the therapy's safety [3]. The compliance of women to hormone replacement therapy has always been poor, due to fear of breast and uterine cancer and the therapy's side effects. The appearance of selective estrogen receptor modulators has given postmenopausal women an alternative. These compounds exert positive effects on bone, with less estrogen-related side effects [4]. Even so, the strong desire for a non-pharmaceutical protective regimen and epidemiological indications of the beneficial effect of certain plants on bone, have led to the study of plant extracts, some of which are named phytoestrogens.
Phytoestrogens are plant compounds with estrogen-like biological activity. The main classes of phytoestrogens are isoflavones, flavonoids, coumestans and lignans. Particularly after consumption of isoflavones and lignans, heterocyclic phenols are formed, which in stereochemical structure are close to estrogen, and have the capacity to bind to the estrogen receptors [5]. Human and animal studies are presently focused on providing convincing data on their potency and method of action in preventing bone loss [6], [7], [8], [9].
A recent phytochemical study of the plant Onobrychis ebenoides showed that two of the three benzofurans isolated had an estrogen receptor binding affinity of 0.29 and 0.28 [10]. This led us to further examine its possible estrogen-like activity in vivo. The aim of the present experimental study was to evaluate the possible beneficial effect of the aforementioned plant's extract on bone loss in the ovariectomized adult rat model of osteoporosis. This model rapidly develops cancellous bone loss in association with an increased bone turnover during the early stages of estrogen deficiency, similar to human menopause. It is a consistent and reproducible model widely used in skeletal research [11], [12], [13]. Additionally, the extract's possible adverse effect on the uterus was also investigated.
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Laboratory animals
The experimental protocol was approved by the General Directorate of Veterinary Services (permit no. K/954/2001), according to Greek legislation (Presidential Decree 160/1991, in compliance to the EEC Directive 609/1986, and Law 2015/1992, in conformance to the “European Convention for the protection of vertebrate animals used for experimental or other scientific purposes, 123/1986”). Forty mature (10-month-old) intact female Wistar rats were obtained from the Hellenic Pasteur Institute,
Bone mineral density absolute values
The bone mineral density measurements carried out pre-ovariectomy and 1, 3 and 6 months post-ovariectomy by DEXA of the three groups of rats are displayed in Table 1, Table 2. Values are in g/cm2. Statistical comparison among groups at the same measurement time of the proximal tibia is shown in Table 1 and of the total tibia in Table 2. It is evident that at 1 month post-ovariectomy there are no differences between groups at both sites examined. At 3 months the total tibia of the treated rats
Discussion
Although hormone replacement therapy has been shown to be effective in prevention and treatment of post-menopausal bone loss, alternatives are continuously being searched because of actual or possible side effects, or contraindications limiting their use, and poor compliance of patients. Selective estrogen receptor modulators act as alternatives, with less estrogen-related side effects and positive effects on bone [4], [15], [16]. Similarly, certain plant compounds, some of which have been
Acknowledgements
The authors wish to thank Ms. M. Katsiri for conducting the bone mass scans, Ms. K. Kalogera for assistance in performing the ovariectomies, Ms. A. Tsiapara for assistance in performing the autopsies and Ms. M. Ioannitou for histomorphometry processing.
This work has been financed by a PAVE grant from the Greek General Secretariat of Research and Technology and the pharmaceutical company PHARMATEN.
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