Effects of tibolone (Org OD14) treatment for 3 months on ovariectomy-induced osteopenia in 8-month-old rats on a low-calcium diet: preventive testing for 3 months

Effects of tibolone on osteoarthritis in ovariectomized rats: association with nociceptive pain behaviour

BACKGROUND

To investigate the role of the synthetic steroid tibolone in the progression of osteoarthritis (OA) and in nociceptive behaviour in an experimental rat model of OA and ovariectomy (OVX)-induced osteoporosis.

METHODS

OA was induced in Wistar rats by anterior cruciate ligament transection (ACLT) of the right knee. Osteoporosis was induced by bilateral OVX. Groups of animals were subjected to ACLT, OVX, sham or OVX + ACLT. In addition, two groups were subjected to OVX + ACLT surgeries and were orally administered 0.1 or 0.5 mg tibolone every other day for 14 consecutive weeks, starting 6 weeks after surgery. Nociceptive behaviours (secondary mechanical allodynia and weight-bearing distribution of the hind paws) were analysed prior to and every 3 weeks after surgery up to 24 weeks. At 24 weeks, histopathological studies were performed on the cartilage and synovial membranes of the knee joints, and bone metabolism was assessed by measuring serum concentrations of calcium, phosphorus and alkaline phosphatase.

RESULTS

Rats undergoing ACLT or OVX + ACLT surgeries showed obvious OA changes in the joints. Animals subjected to ACLT + OVX and treated with tibolone had significantly less cartilage degeneration and synovitis and showed improved nociceptive tests compared with animals undergoing ACLT + OVX surgeries alone. OVX increased the severity of the ACLT-induced OA changes. There was a significant increase in serum alkaline phosphatase in the tibolone-treated ACLT + OVX groups.

CONCLUSIONS

Treatment with tibolone attenuated the development of OA, concomitantly reduced nociception and increased serum alkaline phosphatase in ACLT + OVX rats.

Role of phytoestrogenic oils in alleviating osteoporosis associated with ovariectomy in rats

The objective of this study was to elucidate the effect of soybean oil (SbO) and sesame oil (SO) supplemented diets on bone biomarkers changes in OVX (ovariectomized) rats. The current data exhibited significant decrease in BMD (bone mineral density), accompanied with marked depletion in the level of Ca, P and Mg in both serum and bone of OVX rats. Also, serum estrogen, total protein, HDL-C (high density lipoprotein cholesterol), bone NO levels were decreased in OVX rats. However, a significant increase in the level of serum TL (total lipids), TC (total cholesterol), TG (triglycerides), LDL-C (low density lipoprotein cholesterol), VLDL-C (very low density lipoprotein cholesterol), urine minerals (Ca, P, Mg), as well as serum, bone and urine ALP (alkaline phosphatase) and ACP (acid phosphatase) activity were recorded in OVX rats. Further changes were also detected by the increased level of urine hydroxyproline, serum parathyroid hormone and osteocalcin, as well as urea and creatinine level in both serum and urine. On the other hand, when OVX rats were fed on SbO (soy bean oil) (15 % w/w) or SO (sesame oil) (10 % w/w) supplemented diets, the data recorded a significant improvement in all the above mentioned parameters. So, it can be concluded that consumption of SbO or SO supplemented diets might be considered as a functional food for retarding risks of osteoporosis associated with estrogen deficiency in OVX states.

Perspective on post-menopausal osteoporosis: establishing an interdisciplinary understanding of the sequence of events from the molecular level to whole bone fractures

Current drug treatments for post-menopausal osteoporosis cannot eliminate bone fractures, possibly because the mechanisms responsible for bone loss are not fully understood. Although research within various disciplines has significantly advanced the state of knowledge, fundamental findings are not widely understood between different disciplines. For that reason, this paper presents noteworthy experimental findings from discrete disciplines focusing on post-menopausal osteoporosis. These studies have established that, in addition to bone loss, significant changes in bone micro-architecture, tissue composition and micro-damage occur. Cellular processes and molecular signalling pathways governing pathological bone resorption have been identified to a certain extent. Ongoing studies endeavour to determine how such changes are initiated at the onset of oestrogen deficiency. It emerges that, because of the discrete nature of previous research studies, the sequence of events that lead to bone fracture is not fully understood. In this paper, two sequences of multi-scale changes are proposed and the experimental challenges that need to be overcome to fully define this sequence are outlined. Future studies must comprehensively characterize the time sequence of molecular-, cellular- and tissue-level changes to attain a coherent understanding of the events that ultimately lead to bone fracture and inform the future development of treatments for post-menopausal osteoporosis.

Strength of cancellous bone trabecular tissue from normal, ovariectomized and drug-treated rats over the course of ageing

Hormone therapy (HT) drugs and bisphosphonates prevent osteoporosis by inhibiting osteoclastic bone resorption. However, the effects of osteoporosis and anti-resorptive drugs on the mechanical behavior of the bone tissue constituting individual trabeculae have not yet been quantified. In this study, we test the hypothesis that the mechanical properties of bone trabecular tissue will differ for normal, ovariectomized and drug-treated rat bones over the course of ageing. Microtensile testing is carried on individual trabeculae from tibial bone of ovariectomized (OVX) rats, OVX rats treated with tibolone and placebo-treated controls. The method developed minimizes errors due to misalignment and stress concentrations at the grips. The local mineralization of single trabeculae is compared using micro-CT images calibrated for bone mineral content assessment. Our results indicate that ovariectomy in rats increases the stiffness, yield strength, yield strain and ultimate stress of the mineralized tissue constituting trabecular bone relative to normal; we found significant differences (P < 0.05) at 14, 34 and 54 weeks of treatment. These increases are complemented by a significant increase in the mineral content at the tissue level, although overall bone mineral density and mass are reduced. With drug treatment, the properties remain at, or slightly below, the placebo-treated controls levels for 54 weeks. The higher bone strength in the OVX group may cause the trabecular architecture to adapt as seen during osteopenia/osteoporosis, or alternately it may compensate for loss of trabecular architecture. These findings suggest that, in addition to the effects of osteoporosis and subsequent treatment on bone architecture, there are also more subtle processes ongoing to alter bone strength at the tissue level.

Effects of the steroidal aromatase inhibitor exemestane and the nonsteroidal aromatase inhibitor letrozole on bone and lipid metabolism in ovariectomized rats

PURPOSE

Exemestane (EXE) and letrozole (LET) are third-generation aromatase inhibitors currently prescribed for postmenopausal hormone-dependent breast cancer. The impact on end organs of estrogen depletion in menopausal women is of significant clinical importance. We studied the effects of EXE, its principal metabolite, 17-hydroexemestane (17-H-EXE), and LET on bone and lipid metabolism in ovariectomized (OVX) rats.

EXPERIMENTAL DESIGN

OVX rats were treated by weekly intramuscular injection for 16 weeks with 20, 50, and 100 mg/kg EXE, 20 mg/kg 17-H-EXE, and daily oral gavage of 1 mg/kg LET. At the end of the treatment period, bone mineral density (BMD), the bone resorption marker serum pyridinoline, the bone formation marker serum osteocalcin, bone mechanical properties, histomorphometry, and serum lipid concentrations were determined.

RESULTS

Lumbar vertebral and femoral BMD, bending strength of the femur, compressive strength of the fifth lumbar vertebra, and trabecular bone volume were significantly higher in OVX animals given EXE and 17-H-EXE than in OVX controls. EXE and 17-H-EXE significantly reduced an ovariectomy-induced increase in serum pyridinoline and serum osteocalcin. EXE and 17-H-EXE given to OVX rats caused significant reductions of serum cholesterol and low-density lipoprotein cholesterol. In contrast, OVX rats treated with LET had BMD, bone biomarkers, mechanical failure properties, and lipid levels similar to those of OVX controls.

CONCLUSIONS

EXE and 17-H-EXE significantly prevent bone loss, enhance bone mechanical strength, and lower serum cholesterol and low-density lipoprotein levels in OVX rats. These protective effects on end-organ function are not seen with the nonsteroidal inhibitor LET.

Signal transduction and mechanical stress

Bone undergoes a constant process of remodeling in which mass is retained or lost in response to the relative activity of osteoblasts and osteoclasts. Weight-bearing exercise-which is critical for retaining skeletal integrity-promotes osteoblast function, whereas a lack of mechanical stimulation, as seen during spaceflight or prolonged bed rest, can lead to osteoporosis. Thus, understanding mechanotransduction at the cellular level is key to understanding basic bone biology and devising new treatments for osteoporosis. Various mechanical stimuli have been studied as in vitro model systems and have been shown to act through numerous signaling pathways to promote osteoblast activity. Here, we examine the various types of stress and the sequential response of transduction pathways that result in changes in gene expression and the ensuing proliferation of osteoblasts.

Tibolone exerts its protective effect on trabecular bone loss through the estrogen receptor

Tibolone (Org OD14) has estrogenic, progestogenic, and/or androgenic activity depending on the tissue. In postmenopausal women, tibolone prevents bone loss without stimulating the endometrium. Tibolone is effective in preventing trabecular bone loss from the peripheral and axial skeleton of young and old ovariectomized (OVX) rats by reducing bone turnover, that is, bone resorption, like estrogens. We evaluated the contribution of the various hormonal activities to tibolone's bone-conserving effect. Three-month-old OVX rats received tibolone (125 microg/rat or 500 microg/rat, twice daily), alone or combined with an antiestrogen, antiandrogen, or antiprogestogen, and the effects on trabecular bone mass and bone turnover were evaluated. Sham-operated and control OVX groups were treated with vehicle. The remaining OVX groups received oral doses of tibolone twice daily, alone or with twice daily (a) antiestrogen ICI 164.384, (b) antiandrogen flutamide, or (c) antiprogestogen Org 31710. For comparison, the effects of 17beta-estradiol and testosterone were examined also. After 4 weeks, trabecular bone mineral density (BMD) in the distal femur, plasma osteocalcin, and urinary deoxypyridinoline/creatinine ratio (Dpyr/Cr) were measured. Tibolone or 17beta-estradiol significantly blocked ovariectomy-induced loss of trabecular BMD and inhibited bone resorption and bone turnover as judged by reduced Dpyr/Cr ratio and osteocalcin, respectively. These effects of both compounds were counteracted by the antiestrogen. This suggests a major involvement of the estrogen receptor in the action of tibolone on bone metabolism. However, the antiandrogen and the antiprogestogen did not counteract the effects of tibolone, excluding a major role of the androgenic and progestogenic activities of tibolone in its action against trabecular bone loss. The results indicate that tibolone acts on bone almost entirely through activation of the estrogen receptor.

Effects of 16 weeks of treatment with tibolone on bone mass and bone mechanical and histomorphometric indices in mature ovariectomized rats with established osteopenia on a low-calcium diet

Tibolone is a synthetic steroid with tissue-specific estrogenic, progestogenic, and androgenic properties. The therapeutic effects of tibolone on bone mass and strength, bone metabolic markers, and indices of histomorphometry were investigated in ovariectomized (ovx) rats on a low (0.1%)-calcium diet in comparison with 17alpha-ethynylestradiol (EE) or 1alpha-hydroxyvitamin D3 [1alpha(OH)D3]. Tibolone (0.1-3 mg/kg/day), EE (0.1 mg/kg/day), or 1alpha(OH)D3 (0.5 microg/kg/day) was administered orally once a day for 16 weeks, starting 12 weeks after ovariectomy, when the bone mineral density (BMD) of lumbar vertebrae (L4-5) and femur (global, proximal, and distal regions) had already been decreased by the combination of ovariectomy and low dietary calcium. The BMD of the lumbar vertebrae and the femur were higher in the groups treated with tibolone, EE, or 1alpha(OH)D3 than in the ovx control group. The BMD of the mid-diaphysial regions of femur and tibia, which consist mainly of cortical bone, were decreased 28 weeks after ovariectomy in the ovx control group. The BMD of the mid-diaphysial femur was higher in the groups treated with 1alpha-(OH)D3, and the BMD of mid-diaphysial tibia was higher in the groups treated with tibolone or 1alpha(OH)D3 than in the ovx control group. Like BMD, the compressive strength of the vertebral body of L2, corrected for the volume of each individual vertebra tested, was higher in the groups treated with tibolone, EE, or 1alpha(OH)D3 than in the ovx control group. Trabecular bone volume and trabecular number were reduced 12 and 28 weeks after ovariectomy but there was no change in trabecular thickness. These reduced indices were increased in the groups treated with tibolone, EE, or 1alpha(OH)D3 when compared with the ovx control group. Tibolone or EE decreased serum levels of osteocalcin and bone alkaline phosphatase and urinary levels of deoxypyridinoline and pyridinoline compared with the ovx control group. Furthermore, tibolone or EE decreased the mineralizing surface and bone formation rate as well as the osteoclast surface and osteoclast numbers. 1Alpha(OH)D3, however, did not affect these serum and urinary parameters. These data suggest that tibolone suppresses the accelerated bone turnover induced by a combination of ovariectomy and low dietary calcium, and indicate that tibolone may be a potentially useful drug for the treatment of postmenopausal osteoporosis.