Estradiol treatment transiently increases trabecular bone volume in ovariectomized rats

Estrogen-dependent efficacy of limb ischemic preconditioning in female rats

Our aim was to examine the effects of ischemic preconditioning (IPC) on the local periosteal and systemic inflammatory consequences of hindlimb ischemia-reperfusion (IR) in Sprague-Dawley rats with chronic estrogen deficiency (13 weeks after ovariectomy, OVX) in the presence and absence of chronic 17beta-estradiol supplementation (E2, 20 µg kg^-1 , 5 days/week for 5 weeks); sham-operated (non-OVX) animals served as controls. As assessed by intravital fluorescence microscopy, rolling and the firm adhesion of polymorphonuclear neutrophil leukocytes (PMNs) gave similar results in the Sham + IR and OVX + IR groups in the tibial periosteal microcirculation during the 3-h reperfusion period after a 60-min tourniquet ischemia. Postischemic increases in periosteal PMN adhesion and PMN-derived adhesion molecule CD11b expressions, however, were significantly reduced by IPC (two cycles of 10'/10') in Sham animals, but not in OVX animals; neither plasma free radical levels (as measured by chemiluminescence), nor TNF-alpha release was affected by IPC. E2 supplementation in OVX animals restored the IPC-related microcirculatory integrity and PMN-derived CD11b levels, and TNF-alpha and free radical levels were reduced by IPC only with E2. An enhanced estrogen receptor beta expression could also be demonstrated after E2 in the periosteum. Overall, the beneficial periosteal microcirculatory effects of limb IPC are lost in chronic estrogen deficiency, but they can be restored by E2 supplementation. This suggests that the presence of endogenous estrogen is a necessary facilitating factor of the anti-inflammatory protection provided by limb IPC in females. The IPC-independent effects of E2 on inflammatory reactions should also be taken into account in this model. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:97-105, 2018.

Effects of Chronic Estrogen Administration in the Ventromedial Nucleus of the Hypothalamus (VMH) on Fat and Bone Metabolism in Ovariectomized Rats

Estrogen deficiency after ovariectomy (OVX) results in increased adiposity and bone loss, which can be prevented by systemic 17-β estradiol (E2) replacement. Studies in transgenic mice suggested that in addition to direct actions of estrogen in peripheral tissues, also estrogen signaling in the hypothalamus regulates fat distribution and bone metabolism. We hypothesized that the protective effect of systemic E2 on fat and bone metabolism in the OVX model is partly mediated through the ventromedial nucleus of the hypothalamus (VMH). To test this hypothesis, we determined the effect of systemic, central, and targeted VMH administration of E2 on fat and bone metabolism in OVX rats. Subcutaneous administration of E2 for 4 weeks decreased body weight, gonadal and perirenal fat, and bone formation rate in OVX rats. This effect was completely mimicked by intracerebroventricular injections of E2, once every 4 days for 4 weeks. Administration of E2 locally in the VMH by retromicrodialysis (3 h) acutely increased expression of the lipolytic gene hormone-sensitive lipase in gonadal and perirenal fat. Finally, chronic administration of E2 in the VMH for 8 weeks decreased perirenal fat but did not affect body weight, trabecular bone volume, or cortical thickness. In conclusion, we demonstrated that intracerebroventricular E2 replacement reduces body weight gain, ameliorates intraabdominal fat accumulation, and reduces bone formation in the OVX rats. E2 administration selectively in the VMH also reduced intraabdominal fat but did not affect bone metabolism.

The Protective Effects of Alisol A 24-Acetate from Alisma canaliculatum on Ovariectomy Induced Bone Loss in Vivo

Alisma canaliculatum is a herb commonly used in traditional Korean medicine, and has been shown in scientific studies to have antitumor, diuretic hepatoprotective, and antibacterial effects. Recently, the anti-osteoclastogenesis of alisol A 24-acetate from Alisma canaliculatum was investigated in vitro. However, the influence of alisol A 24-acetate on osteoporosis in animals has not been investigated. The present study was undertaken to investigate the anti-osteoporotic effect of alisol A 24-acetate on bone mass in ovariectomized (OVX) mice and to identify the mechanism responsible for its effects. OVX mice were treated daily with 0.5 or 2 μg/g of alisol A 24-acetate for a period of six weeks. It was found that these administrations significantly suppressed osteoporosis in OVX mice and improved bone morphometric parameters. The serum estradiol, bone alkaline phosphatase levels, regulatory T/Th17 cell numbers were significantly increased by alisol A 24-acetate as compared with untreated OVX mice. In addition, TRAP activity was inhibited by alisol A 24-acetate in OVX mice. These results suggest alisol A 24-acetate effectively prevents bone loss in OVX mice, and that it can be considered a potential therapeutic for the treatment of postmenopausal osteoporosis.

A high-fat diet increases body weight and circulating estradiol concentrations but does not improve bone structural properties in ovariectomized mice

Bone health is influenced by body mass and estrogen. The objective of the study was to determine whether high-fat diet-induced obesity affects bone structure and alters markers of bone turnover in ovariectomized (OVX) mice. We hypothesized that a high-fat diet would increase body weight gain and serum estradiol levels in OVX mice but would not improve bone structural parameter in OVX mice. Thirty-five C57BL/6 mice were either sham operated or OVX at the age of 4 months and then fed either a normal-fat diet (10% energy as fat) or a high-fat diet (45% energy as fat with extra fat from lard) ad libitum for 11 weeks. Ovariectomy increased body weight, serum tartrate-resistant acid phosphatase concentration, and expression of cathepsin K in bone; decreased serum estradiol concentration; and induced significant bone loss manifested by decreased bone volume/total volume (BV/TV), connectivity density (Conn.D), trabecular number, and trabecular thickness with increased trabecular separation and structural model index (P < .01). The high-fat diet increased body weight (P < .01) in OVX mice and nonsignificantly decreased BV/TV (P = .08) and Conn.D (P = .10). Despite having similar serum estradiol concentrations and higher body weight, OVX mice consuming the high-fat diet had lower BV/TV, Conn.D, trabecular number, trabecular thickness, and higher structural model index and trabecular separation than did sham mice fed the normal-fat diet. These findings indicate that increased body weight and elevated serum estradiol concentration induced by a high-fat diet do not mitigate ovariectomy-induced bone loss in mice.

Estradiol favors glucose oxidation in gastrocnemius muscle through modulation of insulin signaling molecules in adult female rats

INTRODUCTION

Estrogens are steroid compounds that are synthesized in ovary, testis, adrenal cortex and other tissues. Several surveys have shown the potential relationship between estradiol and glucose homeostasis in physiological and pathological states such as the menstrual cycle, gestation, gestational diabetes mellitus and polycystic ovarian syndrome (PCOS). All these states are characterized by variability in estradiol level and some degree of insulin resistance. Skeletal muscle plays a crucial role in maintaining systemic glucose metabolism through activation of assorted signaling molecules.

OBJECTIVES

The present study is to evaluate the aftermath of ovariectomy and estradiol replacement on few insulin signaling molecules and GLUT4 protein expression and glucose oxidation in gastrocnemius muscle of adult albino rat.

DESIGN

In the present study, Wistar strain albino rats were selected and divided into three groups. Group I: Control (sham-operated). Group II: Ovariectomized and Group III: Estradiol was replaced 7 days after ovariectomy at a dose of 6 μg/kg boxpression of insulin signaling molecules (western blot) and glucose oxidation were assessed.

RESULTS

Ovariectomy significantly depleted the expression of insulin signaling molecules and glucose oxidation whereas estradiol replacement improved them. Thus, estradiol helps in maintaining glucose level in ovariectomized rats. Results of this study suggest that estradiol improves the expression of insulin signaling molecules in skeletal muscle and thereby it prevents the onset of insulin resistance as a result of estradiol deficiency.

In vivo calcium and phosphate iontophoresis for the topical treatment of osteoporosis

BACKGROUND

In addition to systemic treatment, osteoporosis may be treated topically by incorporating calcium and phosphate into the bone.

OBJECTIVE

This article describes the use of a recently developed, novel iontophoretic apparatus suitable for local ion delivery into bones. In this study, in vivo experiments were performed to compare the effects of local electrotherapy and those of systemic hormone replacement on bone.

DESIGN

In this study, local iontophoresis was carried out in ovariectomized and control rats. Bone density, biomechanical, and elemental studies were performed.

METHODS

Forty 12-week-old Sprague-Dawley rats received an ovariectomy (OVX) or were sham-operated (sham). Twenty-one weeks later, tibias of subgroups of sham-operated and OVX animals were subjected to serial local iontophoresis (IOP) treatments, received systemic subcutaneous 17β-estradiol (E2), or were treated with the combination of IOP and E2. Changes in bone density were detected by quantitative ultrasound densitometry and expressed as amplitude-dependent speed of sound (AD-SoS). Biomechanical studies and elemental analysis were performed at the end of the experiments.

RESULTS

Osteopenia developed 21 weeks after OVX in the proximal tibial regions; the mean difference estimate (95% confidence intervals) of AD-SoS values between the sham-operated and OVX animals was 188.7 (140.4-237.1). Serial iontophoretic treatment resulted in an increase in bone density in both sham-operated and OVX animals (sham+IOP versus sham: 121.4 [73.01-169.7]; OVX+IOP versus OVX: 241.6 [193.2-289.9]). Similar changes in AD-SoS were detected after 17β-estradiol (E2) treatment; however, even greater changes occurred after OVX+E2+IOP versus OVX+E2 (123.4 [75.1-171.8]). Similar improvements also were evident regarding the biomechanical features of the tibias.

LIMITATIONS

A limitation of this study was the relatively small number of rats.

CONCLUSIONS

The efficacy of local IOP using calcium- and phosphate-donating microparticles is comparable to that of estrogen therapy as evidenced by steadily increasing bone density, restoration of the calcium and phosphate balance, and improvement in the biomechanical properties of the bone.

Influence of estrogen deficiency on bone around osseointegrated dental implants: an experimental study in the rat jaw model

PURPOSE

The aim of this study was to evaluate the influence of estrogen deficiency on bone around osseointegrated dental implants in a rat jaw model.

MATERIALS AND METHODS

This study used 16 female rats that had the first molars bilaterally extracted and were allowed to heal for 30 days before implant placement. Sixty days after implant placement, the animals were randomly subjected to sham surgery or ovariectomy (OVX). The animals were euthanized 90 days after OVX. Bone-to-implant contact, bone area fraction occupancy between implant threads, mineral density, turnover markers, and cells positive for tartrate-resistant acid phosphatase were assessed for the 2 groups.

RESULTS

The results showed that OVX group presented a decrease of systemic bone density, alterations in bone turnover markers, and an increase of cells positive for tartrate-resistant acid phosphatase compared with the sham-surgery group. However, no difference relative to bone-to-implant contact and bone area fraction occupancy was observed between groups.

CONCLUSIONS

The findings of this study demonstrate that estrogen deficiency may not be considered a risk factor for osseointegrated implant failure in jaw bone.

Periosteal microcirculatory action of chronic estrogen supplementation in osteoporotic rats challenged with tourniquet ischemia

AIMS

Transient ischemia of osteoporotic bones during elective orthopedic surgery or fracture repair carries risks for serious complications, and estrogen loss or replacement has a potential to influence ischemia-reperfusion-induced inflammatory activation. To clarify this, we investigated the periosteal inflammatory changes in a clinically relevant time frame in ovariectomized rats, an experimental model of postmenopausal bone loss. Furthermore, the effects of chronic estrogen supplementation on the postischemic local and systemic inflammatory reactions were assessed.

MAIN METHODS

Bilateral ovariectomy or sham operation was performed in 3-month-old female Sprague-Dawley rats. Five months later, estrogen replacement therapy with 17β-estradiol (20 μg(-1) kg(-1) day(-1)) or vehicle treatment was initiated. The microcirculatory inflammatory consequences of 60-min total hindlimb ischemia followed by 180-min reperfusion were examined 11 months after ovariectomy and were compared with those in 3-month-old animals.

KEY FINDINGS

The osteoporosis that developed 5 months after ovariectomy was significantly ameliorated by estrogen replacement therapy. Both in ovariectomized and in non-ovariectomized animals, ischemia-reperfusion elevated the neutrophil adherence ~3-fold in the postcapillary venules of the periosteum (intravital microscopy), with an ~50-60% increase in intravascular neutrophil activation (CD11b; FACS analysis), an enhanced TNF-α release (ELISA) and periosteal expression of ICAM-1 (the endothelial ligand of CD11b; immunohistochemistry). Exogenous 17β-estradiol considerably reduced TNF-α release and the number of neutrophil-endothelial interactions in the periosteum, without affecting the CD11b and ICAM-1 expression changes.

SIGNIFICANCE

Osteoporosis itself does not increase the magnitude of the limb ischemia-reperfusion-associated periosteal inflammatory reaction. Chronic estrogen supplementation, however, reverses osteoporosis and significantly ameliorates the microcirculatory consequences of transient ischemia.

The effect of oestrogen and alendronate therapies on postmenopausal bone loss around osseointegrated titanium implants

OBJECTIVES

This study evaluated the influence of oestrogen deficiency and its therapies on bone tissue around osseointegrated implants.

METHODS

Implants were placed in 66 female rats tibiae. The animals were assigned into five groups: control (CTL), sham, ovariectomy (OVX), oestrogen (EST), and alendronate (ALE). While CTL was sacrificed 60 days after implant placement, other groups were subjected to ovariectomy or sham surgery according to group and euthanized after 90 days. Blood and urine samples were collected at sacrifice day for osteocalcin (OCN) and deoxypyridinoline (DPD) quantification. Densitometry of femur and lumbar vertebrae was performed in order to evaluate rats' skeletal impairment. Non-decalcified sections were referred to fluorescent and light microscopy for analyses of mineral apposition rate (MAR), eroded and osteoclastic surfaces, bone-to-implant contact (BIC), and bone area fraction occupancy (BAFO).

RESULTS

Results from the OVX group showed significantly lower bone mineral density (BMD), BIC, BAFO, and MAR, while OCN, deoxipiridinoline, eroded surface and ostecoclastic surface were increased compared with the other groups of the study. ALE reduced OCN and DPD concentrations, MAR, osteoclastic and eroded surfaces, and no difference was in BIC and BAFO relative to SHAM. EST and CTL showed similar results to SHAM for measurements.

CONCLUSIONS

Oestrogen deficiency exerted a negative influence on bone tissue around implants, while oestrogen replacement therapy and alendronate were effective against its effects. Although alendronate therapy maintained the quantity of bone around implants, studies evaluating bone turnover kinetics are warranted.

Identification of genes influencing skeletal phenotypes in congenic P/NP rats

We previously showed that alcohol-preferring (P) rats have higher bone density than alcohol-nonpreferring (NP) rats. Genetic mapping in P and NP rats identified a major quantitative trait locus (QTL) between 4q22 and 4q34 for alcohol preference. At the same location, several QTLs linked to bone density and structure were detected in Fischer 344 (F344) and Lewis (LEW) rats, suggesting that bone mass and strength genes might cosegregate with genes that regulate alcohol preference. The aim of this study was to identify the genes segregating for skeletal phenotypes in congenic P and NP rats. Transfer of the NP chromosome 4 QTL into the P background (P.NP) significantly decreased areal bone mineral density (aBMD) and volumetric bone mineral density (vBMD) at several skeletal sites, whereas transfer of the P chromosome 4 QTL into the NP background (NP.P) significantly increased bone mineral content (BMC) and aBMD in the same skeletal sites. Microarray analysis from the femurs using Affymetrix Rat Genome arrays revealed 53 genes that were differentially expressed among the rat strains with a false discovery rate (FDR) of less than 10%. Nine candidate genes were found to be strongly correlated (r(2) > 0.50) with bone mass at multiple skeletal sites. The top three candidate genes, neuropeptide Y (Npy), alpha synuclein (Snca), and sepiapterin reductase (Spr), were confirmed using real-time quantitative PCR (qPCR). Ingenuity pathway analysis revealed relationships among the candidate genes related to bone metabolism involving beta-estradiol, interferon-gamma, and a voltage-gated calcium channel. We identified several candidate genes, including some novel genes on chromosome 4 segregating for skeletal phenotypes in reciprocal congenic P and NP rats.

Assessment of estradiol influence on spatial tasks and hippocampal CA1 spines: evidence that the duration of hormone deprivation after ovariectomy compromises 17beta-estradiol effectiveness in altering CA1 spines

Two pulses of 17beta-estradiol (10 microg) are commonly used to increase hippocampal CA1 apical dendritic spine density and alter spatial performance in ovariectomized (OVX) female rats, but rarely are the measures combined. The goal of this study was to use this two-pulse injection protocol repeatedly with intervening wash-out periods in the same rats to: 1) measure spatial ability using different tasks that require hippocampal function and 2) determine whether ovarian hormone depletion for an extended 10-week period reduces 17beta-estradiol's effectiveness in elevating CA1 apical dendritic spine density. Results showed that two injections of 10 microg 17beta-estradiol (72 and 48 h prior to testing and timed to maximize CA1 apical spine density at behavioral assessment) corresponded to improved spatial memory performance on object placement. In contrast, two injections of 5 microg 17beta-estradiol facilitated spatial learning on the water maze compared to rats given two injections of 10 microg 17beta-estradiol or the sesame oil vehicle. Neither 17beta-estradiol dose altered Y-maze performance. As expected, the intermittent two-pulse injection protocol increased CA1 apical spine density, but 10 weeks of OVX without estradiol treatment decreased the effectiveness of 10 microg 17beta-estradiol to increase CA1 apical spine density. Moreover, two pulses of 5 microg 17beta-estradiol injected intermittently failed to alter CA1 apical spine density and decreased basal spine density. These results demonstrate that extended time without ovarian hormones reduces 17beta-estradiol's effectiveness to increase CA1 apical spine density. Collectively, these findings highlight the complex interactions among estradiol, CA1 spine density/morphology, and task requirements, all of which contribute to behavioral outcomes.

Influence of estrogen deficiency and its treatment with alendronate and estrogen on bone density around osseointegrated implants: radiographic study in female rats

OBJECTIVE

This study evaluated the influence of estrogen deficiency and its treatment on bone density around integrated implants.

STUDY DESIGN

Implants were placed in female rat tibiae. The animals were assigned to 5 groups: control, sham, ovariectomy, estrogen, and alendronate. The control group was humanely killed to confirm integration of the implant. The others were submitted to ovariectomy or sham surgery. Bone density was measured by digital radiographs at 6 points on sides of the implant.

RESULTS

The analysis of radiographic bone density revealed estrogen privation had a negative impact only in the cancellous bone. The estrogen group differed significantly (P < .05) from the ovariectomy and alendronate groups. The alendronate group presented the highest density for all evaluated regions.

CONCLUSION

Ovariectomy caused a decrease in the radiographic bone density in the cancellous region. Estrogen replacement therapy and alendronate were effective treatments in preventing bone mass loss around integrated implants.

Additional weight bearing during exercise and estrogen in the rat: the effect on bone mass, turnover, and structure

Mechanical loading and estrogen play important roles in bone homeostasis. The aim of this study was to evaluate the effects of mechanical loading on trabecular bone in the proximal femur of ovariectomized rats. We hypothesized that mechanical loading suppresses bone resorption and increases bone formation, which differs from the suppressive effects of estrogen on both resorption and formation. Furthermore, we expected to find changes in trabecular architecture elicited by the effects of mechanical loading and estrogen deficiency. Sixty female Wistar rats, 12 weeks old, were assigned to either the sedentary groups sham surgery (SED), ovariectomy (SED+OVX), and ovariectomy with estrogen replacement (SED+OVX+E2) or to the exercise groups EX, EX+OVX, EX+OVX+E2. Following ovariectomy, 5 microg 17beta-estradiol was given once weekly to the estrogen replacement groups. Exercise consisted of running with a backpack (load +/-20% of body weight) for 15 minutes/day, 5 days/week, for 19 weeks. Dual-energy X-ray absorptiometry (DXA) scans were performed before (T0), during (T6), and after (T19) the exercise period to obtain bone mineral content (BMC) and bone mineral density (BMD) data. After the exercise program, all rats were killed and right and left femora were dissected and prepared for micro-CT scanning and histomorphometric analysis of the proximal femoral metaphysis. After 19 weeks, increases in BMC (P = 0.010) and BMD (P = 0.031) were significant. At T19, mechanical loading had a significant effect on BMC (P = 0.025) and BMD (P = 0.010), and an interaction between mechanical loading and estrogen (P = 0.023) was observed. Bone volume and trabecular number decreased significantly after ovariectomy, while trabecular separation, mineralizing surface, bone formation rate, osteoclast surface, degree of anisotropy, and structure model index increased significantly after ovariectomy (P < 0.05). Trabecular bone turnover and structural parameters in the proximal femur were not affected by exercise. Estrogen deficiency resulted in a less dense and more oriented trabecular bone structure with increased marrow cavity and a decreased number of trabeculae. In conclusion, mechanical loading has beneficial effects on BMC and BMD of the ovariectomized rat. This indicates that the load in the backpack was high enough to elicit an osteogenic response sufficient to compensate for the ovariectomy-induced bone loss. The results confirm that estrogen suppresses both bone resorption and bone formation in the proximal metaphysis in the femoral head of our rat-with-backpack model. The effects of mechanical loading on the trabecular bone of the femoral head were not significant. This study suggests that the effect of mechanical loading in the rat-with-backpack model mainly occurs at cortical bone sites.

In vitro evaluation of the direct effect of estradiol on human osteoblasts (HOB) and human mesenchymal stem cells (h-MSCs)

Estrogen may increase the proliferation of osteoblasts depending upon their differentiation stage. Our objective was to test the hypothesis that estradiol could stimulate the proliferation of primary human osteoblast (HOB) cells or human mesenchymal stem cells (h-MSCs). To test this hypothesis, we investigated two synthetic estradiol preparations: (a) a commercially available one (in clinical use) whose effect was evaluated using MTT assay, trypan blue cell counts and total protein assays; (b) a novel synthetic preparation (not in clinical use) using Alamar Blue assays and scanning electron microscopy (SEM). Commercial estradiol increased HOB proliferation in a concentration-dependant manner between 1 nM and 8 nM reaching significance at a concentration of 8 nM (p<0.001). Small doses of 1 nM and 2 nM increased h-MSC proliferation (p<0.001) but higher doses had no effect. All novel synthetic estradiol preparations decreased HOB proliferation (p<0.001) whereas no direct effect was observed on h-MSCs. Commercial estradiol appears to induce proliferation of HOBs, although its effects on h-MSCs appears to be highly dose-dependent and requires further investigation.

Effect of Cigarette Smoke Inhalation and Estrogen Deficiency on Bone Healing Around Titanium Implants: A Histometric Study in Rats

BACKGROUND

It has been shown that cigarette smoke inhalation (CSI) and estrogen deficiency (OVX) may affect bone quality around titanium implants; however, their association has not been evaluated. Therefore, this study aimed to verify the effects of CSI associated with OVX on bone healing around titanium implants.

METHODS

The tibia surface of 45 female Wistar rats was surgically exposed, and screw-shaped titanium implants were placed. The animals were randomly assigned to OVX (ovariectomized rats; n = 15), SHAM (sham-operated rats; n = 15), and CSI + OVX (4 months of intermittent cigarette smoke inhalation, starting 2 months before implant placement in ovariectomized rats; n = 15). The implants were placed at the time of OVX or SHAM surgery. After 60 days, the animals were sacrificed and undecalcified sections obtained. The percentages of mineralized tissue (bone density [BD]) in a 500-microm-wide zone lateral to the implant, bone filling (BF) within the limits of the threads, and bone-to-implant contact (BIC) were measured in cortical (zone A) and cancellous (zone B) bone.

RESULTS

In zone A, the CSI + OVX group showed a significant difference regarding BIC and BD (P <0.05) compared to the other groups. In zone B, data analysis showed that the CSI + OVX group presented the lowest percentage of BD and BIC, followed by the OVX and SHAM groups, respectively (P <0.05).

CONCLUSION

Within the limits of the present study, it can be concluded that cigarette smoke inhalation amplified the deleterious effects of estrogen deficiency, affecting both preexisting and newly formed bone in the cortical and cancellous bone around titanium implants.

Alendronate Therapy May Be Effective in the Prevention of Bone Loss Around Titanium Implants Inserted in Estrogen-Deficient Rats

BACKGROUND

This study evaluated whether alendronate (ALD) influences bone healing around titanium implants inserted in ovariectomized rats and whether it provides a residual effect after its withdrawal.

METHODS

Bilateral ovariectomies were performed in 87 Wistar rats and one screw-shaped titanium implant was placed in the tibiae. The animals were divided into the following groups: group SHAM (N = 15): sham surgeries; group OVX (N = 15): ovariectomy; group AT (N = 15): OVX plus alendronate administration for 80 days; group AW (N = 14): OVX plus alendronate administration for 40 days; group ET (N = 14): OVX plus 17beta estradiol administration for 80 days; or group EW (N = 14): OVX plus 17beta estradiol administration for 40 days. Bone-to-implant contact (BIC), bone area (BA) within the limits of implant threads, and bone density in a 500 microm-wide zone lateral to the implant (BD) were obtained and measured for the cortical (zone A) and cancellous (zone B) regions.

RESULTS

In zone A, data analysis showed no significant differences among the groups regarding BIC and BD (P >0.05), and a slight beneficial effect of estradiol on BA when compared with the OVX, EW, and AW groups (P <0.05). In zone B, OVX negatively impacted bone healing around the implants, resulting in reduced BA and BD (P<0.05). ALD (continuous/interrupted) and estradiol (only continuous) positively affected BIC, BA, and BD, resulting in values at the same level as the control group (SHAM).

CONCLUSIONS

ALD may prevent the negative influence of estrogen deficiency on bone healing around titanium implants inserted in OVX rats. This positive effect, in contrast to estradiol, is sustained following its withdrawal.

Lifetime high calcium intake increases osteoporotic fracture risk in old age

Caloric restriction prolongs life span. Calcium restriction may preserve bone health. In osteoporosis, bone mineral density (BMD) has significantly decreased, due to a lack of osteoblast bone formation. Traditional osteoporosis prevention is aimed at maximizing BMD, but the lifetime effects of continuously maintaining a high BMD on eventual bone health in old age, have not been studied. Strikingly, in countries with a high mean BMD, fracture rates in the elderly are significantly higher than in countries with a low mean BMD. Studies show that this is not based on genetic differences. Also, in primary hyperparathyroidism, on the brink of osteoporosis, BMD levels may be significantly higher than normal. Maybe, BMD does not represent long term bone health, but merely momentary bone strength. And maybe, maintaining a high BMD might actually wear out bone health. Since osteoporosis particularly occurs in the elderly, and because in osteoporotic bone less osteoblasts are available, the underlying process may have to do with ageing of osteoblastic cells. In healthy subjects, osteoblastic bone cells respond to the influx of calcium by composing a matrix upon which calcium precipitates. In the process of creating this matrix, 50-70% of the involved osteoblasts die. The greater the influx of calcium, the greater osteoblast activity, and the greater osteoblast apoptosis rate. An increased osteoblast apoptosis rate leads to a decrease in the age-related osteoblast replicative capacity (ARORC). In comparison to healthy bone, in osteoporotic bone the decrease in the replicative capacity of osteoblastic cells is greater. Due to the eventual resulting lack of osteoblast activity, micro-fractures cannot be repaired. Continuously maintaining a high BMD comes with continuously high bone remodeling rates, which regionally exhaust the ARORC, eventually leading to irreparable microfractures. Regarding long time influences on bone health, adequate estrogen levels are known to be protective against osteoporosis. This is generally attributed to its inhibiting influence on osteoclast activity. Instead, its net effects on osteoblast metabolism may be the key to osteoporosis prevention. Adequate estrogen levels inhibit osteoblast activity, calcium apposition and osteoblast apoptosis rate, preserving the ARORC.

CONCLUSION

Regarding osteoporosis prevention, ARORC better than BMD represents bone health. Regarding ARORC, adequate estrogen levels are protective, opposing the similar effects of hyperparathyroidism and a high calcium diet. Tests need to be performed in mice to assess the lifetime effects of a high versus a low calcium diet, on eventual bone fracture toughness.

Differential transcriptional effects of PTH and estrogen during anabolic bone formation

The aim of this study was to compare transcriptional regulation in vivo during anabolic bone formation induced by either estradiol (E2) treatment or intermittent parathyroid hormone[1-34] (PTH) therapy. We utilized an ovariectomized (OVX) mouse model of osteoporosis and transcriptional profiling to identify genes upregulated by either high-dose E2 or PTH. Five weeks post-OVX, the mice were administered either E2 and/or PTH, or vehicle for 4 weeks. Femoral bones were analyzed by microCT and histomorphometry to confirm the anabolic effect of each treatment. OVX vehicle-treated control mice lost metaphyseal trabecular bone, with significant decrease in trabecular number, thickness, and connectivity. Both E2 and PTH treatments increased trabecular and cortical bone indices above the level of the sham operated controls, fully restoring both bone volume and bone mineral density (BMD). Moreover, PTH/E2 combination treatment led to significantly greater increase in cancellous bone and BMD than would be expected from the additive effects of the separate treatments. To determine whether PTH and E2 treatments were stimulating similar bone anabolic mechanisms, or were activating distinct signaling pathways, we compared patterns of gene expression using transcriptional profiling after either E2 or PTH treatment. After 4, 11, and 24 days of treatment, total RNA was collected from both the distal femoral metaphysis and diaphysis. Transcriptional profiling was performed using Affymetrix GeneChip probe arrays, comprised of approximately 36,000 full-length mouse genes and EST clusters from the UniGene database. Several markers of osteoblast activity, including c-fos, RANKL, PHEX, and PTHR1, were consistently upregulated by PTH in both skeletal sites. PTH treatment also increased expression of Cathespin K, consistent with the predicted increase in osteoclast activity. E2 treatment upregulated a largely distinct set of genes, including TGFbeta3, and BMP1, as well as several genes critical for cell cycle control, including Cyclin D1 and CDK inhibitor 1A. Overall, comparison of transcriptional profiles suggest that anabolic responses in bone to PTH and high-dose E2 treatment after OVX-induced osteoporosis involve largely distinct patterns of gene regulation, each resulting in restoration of bone mass.

Effect of estrogen and calcitonin therapies on bone density in a lateral area adjacent to implants placed in the tibiae of ovariectomized rats

BACKGROUND

This study evaluated the influence of estrogen and calcitonin administration on tibial bone density in a lateral area adjacent to implants placed in ovariectomized rats (OVX).

METHODS

One screw-type titanium implant was placed bilaterally in the ovariectomized rats, and the animals assigned to one of the following groups: group 1 (n = 15): sham surgeries; group 2 (n = 15): OVX; group 3 (n = 14): OVX subcutaneously administered with calcitonin (CT) 4 days/week (16 IU/kg); group 4 (n = 14): OVX administered daily with 17beta estradiol (20 microg/kg). After 60 days, the animals were sacrificed and undecalcified sections obtained. Blood samples were collected to measure serum levels of alkaline phosphatase and calcium at the time of sacrifice. Bone density was measured in a 500 microm wide mineralized zone lateral to the implant.

RESULTS

Alkaline phosphatase levels in groups 2 and 3 (P > 0.05) were statistically higher than groups 1 and 4 (P < 0.05), and calcium serum levels were higher in group 2 than the other groups (P < 0.05). Regarding bone density, the data were grouped separately for cortical (zone A) and cancellous (zone B) bone. In zone A, intergroup analysis revealed no significant difference among groups (P > 0.05). However, in zone B, the animals that received estrogen administration (group 4) presented a higher bone density than groups 2 and 3 (P < 0.05).

CONCLUSION

It appears that estrogen therapy may prevent the negative influence of endogenous estrogen deficiency on bone density around titanium implants placed in ovariectomized rats.

Effects of ovariectomy and estrogen replacement therapy on arthritis and bone mineral density in rats with collagen-induced arthritis

We investigated the effects of ovariectomy (ovx) and estrogen replacement therapy (ERT) on bone mineral density (BMD) and arthritis severity in rats with collagen-induced arthritis (CIA). Seven-month-old female Sprague-Dawley rats were separated into a sham group (n = 8), CIA group (n = 14), ovx group (n = 10), CIA + ovx group (n = 11), and CIA + ovx + ERT group (n = 14). In these groups, ovx was performed at 7 days, and ERT (17beta-estradiol at 20 microg/kg three times per week) was initiated 8 days after sensitization. Every 2 weeks, until 8 weeks after sensitization, arthritis score and hind paw thickness were evaluated, and BMD of the trabecular and cortical bones in the metaphysis and diaphysis of the tibia were measured by peripheral quantitative computed tomography. The arthritis score was highest in the CIA + ovx group at all timepoints after sensitization. The hind paw thickness was significantly higher in the CIA + ovx group than in the CIA group at 8 weeks after sensitization (p < 0.05). Both the arthritis score and hind paw thickness were lower in the CIA + ovx + ERT group than in the CIA + ovx group. BMD in the metaphysis was significantly decreased in both the trabecular and cortical bones in the CIA + ovx group compared with those in the CIA group at 4, 6, and 8 weeks after sensitization. In the CIA + ovx group, trabecular BMD was changed by -34 +/- 11%, and cortical BMD changed by -14 +/- 7% in the metaphysis at 8 weeks compared with those at 0 week. In the CIA group, changes of BMD in the metaphysis were -7 +/- 11% in trabecular bone and 0 +/- 7% in cortical bone. These differences of trabecular and cortical bone loss in the metaphysis were significant (both p < 0.01). BMD reduction was significantly less in the CIA + ovx + ERT group than in the CIA + ovx group at 6 and 8 weeks after sensitization. Although BMD in the diaphysis was also reduced in the groups with CIA, the degree of reduction was smaller than in the metaphysis. We conclude that ovx in CIA rats could enhance the severity of arthritis and bone loss, and that ERT could suppress arthritis and bone loss.

Oestrogen and essential fatty acid supplementation corrects bone loss due to ovariectomy in the female Sprague Dawley rat

Essential fatty acid deficient animals develop osteoporosis. Eicosapentaenoic acid and gamma-linoleic acid have been reported to have positive effects on bone metabolism in both the growing male rat and the ovariectomized (OVX) female rat. These effects have been further investigated using a novel gamma-linolenic/eicosapentaenoic acid diester together with an oestrogen implant in the ovariectomized, female Sprague Dawley rat. Rats were sham-operated or ovariectomized at age 11 weeks. Two groups of OVX rats received an oestrogen implant at ovariectomy. Animals received fatty acids, linoleic acid (control) or a diester with gamma-linolenic acid and eicosapentaenoic acid as part of a semi-synthetic diet. Bone calcium content and excretion of deoxypyridinolines as marker of bone degradation were measured at 14 weeks. Oestrogen, as well as diester alone, increased calcium/femur to sham levels. Oestrogen plus diester potentiated the effect of oestrogen on bone calcium (P < 0.05 vs OVX). At the same time, oestrogen alone and the combination of oestrogen plus diester significantly reduced (P < 0.05 vs OVX) urinary deoxypyridinoline and hydroxyproline excretion. Again, the diester potentiated the effect of oestrogen. The effects of the diester alone, together with the potentiated effects of oestrogen by the essential fatty acids on osteoporosis, are novel findings.

Early effects of hormone replacement therapy on bone

Estrogen replacement is currently the preferred therapy for postmenopausal osteoporosis, although its mechanism of action remains poorly understood. Its primary action on bone is generally considered to be antiresorptive, but there is evidence in animals to suggest a stimulatory effect on bone formation. We have now attempted to detect a similar effect in humans by administering hormone replacement therapy (estradiol valerate 2 mg/day and dydrogesterone 5 mg/day given in a continuous, combined manner) to ten postmenopausal women. We carried out histomorphometric analyses of transiliac bone biopsies after quadruple tetracycline labeling, which was commenced before and continued during the first 4 weeks of hormone replacement therapy. Biochemical markers of bone turnover suggested that bone resorption decreased, but no significant effects on histomorphometric parameters of bone formation were detected. We conclude that hormone replacement therapy at the dose given does not stimulate bone formation in the iliac crest as assessed by histomorphometry.

Early estrogen replacement therapy reverses the rapid loss of trabecular bone volume and prevents further deterioration of connectivity in the rat

To evaluate the ability of estrogen replacement therapy (ERT) to prevent changes in trabecular bone volume (BV/TV) and connectivity beginning either at ovariectomy (OVX) or 5-13 days after OVX in adult female rats, the right proximal tibial was examined by three-dimensional X-ray tomographic microscopy (XTM) in vivo. Animals had XTM scans of the right tibia and then were randomized into six groups (n = 9). Groups 2-6 had bilateral (OVX), while group 1 was sham-ovariectomized (OVXd) on day 0. Animals were treated with vehicle (groups 1 and 2) or 17beta-estradiol therapy (ERT) at 10 microg/kg three times per week starting at days 0, 5, 8, and 13 post-OVX (groups 3, 4, 5, and 6), until day 50 when they were rescanned by XTM and sacrificed. Trabecular bone structural variables were calculated from XTM data (BV/TVx and beta1/BV/TVx) and standard histomorphometry. Trabecular bone volume (BV/TVx) and the trabecular connections per cubic millimeter of trabecular bone (beta1/BV/TVx) were maintained in both sham-OVXd animals and OVX animals given ERT from the time of OVX. However, OVX + vehicle-treated animals lost 54% BV/TVx and 46% beta1/BV/TVx (p < 0. 01 from day 0). BV/TVx and beta1/BV/TVx decreased rapidly post-OVX to -22% and -25% at day 13 (p < 0.01 from day 0). ERT initiated at day 5, 8, and 13 post-OVX restored BV/TVx to baseline values at day 50 by modestly increasing trabecular plate thickness; however, beta1/BV/TVx was reduced in all OVX groups when compared with their baseline values. ERT also caused a significant reduction in bone turnover compared with OVX + vehicle; however, resorption was suppressed more than formation. These results demonstrate that ERT can restore the lost trabecular bone, but not trabecular connectivity, that occurs soon after OVX by allowing bone formation to continue in previously activated bone remodeling units while suppressing the production of new remodeling units. This may be the mechanism by which prompt intervention with estrogen and other antiresorptive agents can restore bone mass that has been lost from the increase in remodeling space, and thereby reduce the risk of osteoporotic fractures in postmenopausal women.

Variation in the short-term changes in bone cell activity in three regions of the distal femur immediately following ovariectomy

The effect of ovariectomy (OVX) on cancellous bone in the rat is not uniform at all sites of the skeleton. We report variation in the short-term effects of adult OVX in three regions of the distal femur: the diaphysis (DIA), the metaphysis (META), and the epiphysis (EPI). Cancellous bone parameters were estimated in the three separate zones of the femora and compared with changes in bone cell activity, as estimated by osteoclast surface (Oc.S) and bone formation rate (BFR). Changes were studied for 30 days in a series of rats either sham-operated (Sham) or ovariectomized (OVX) at 7 months of age. Oc.S and BFR were elevated following OVX in all regions. The time course for the OVX-induced changes differed between regions: DIA, both Oc.S and BFR were elevated at day 9; META, Oc.S was also elevated at day 9, while the rise in BFR was delayed until day 21; EPI, Oc.S remained stable but increased relative to ovary-intact rats by day 18 due to reduced levels in the latter, but BFR did not rise until day 28. These changes in bone cell activity following OVX produced a 71% reduction of cancellous bone in the DIA and a 35% reduction in the META. In contrast, no OVX-induced bone loss was observed in the EPI. This study shows that bone cell activity increases in each region of the distal femur within the first 30 days following OVX, independent of bone loss. However, the time course of increased bone cell activity is not uniform. These data highlight the role of local factors in the response to ovarian hormone deficiency.