Dietary dried plum increases bone mass, suppresses proinflammatory cytokines and promotes attainment of peak bone mass in male mice

Nutrition is an important determinant of bone health and attainment of peak bone mass. Diets containing dried plum (DP) have been shown to increase bone volume and strength. These effects may be linked to the immune system and DP-specific polyphenols. To better understand these relationships, we studied DP in skeletally mature (6-month-old) and growing (1- and 2-month-old) C57Bl/6 male mice. In adult mice, DP rapidly (<2 weeks) increased bone volume (+32%) and trabecular thickness (+24%). These changes were associated with decreased osteoclast surface (Oc.S/BS) and decreased serum CTX, a marker of bone resorption. The reduction in Oc.S/BS was associated with a reduction in the osteoclast precursor pool. Osteoblast surface (Ob.S/BS) and bone formation rate were also decreased suggesting that the gain in bone in adult mice is a consequence of diminished bone resorption and formation, but resorption is reduced more than formation. The effects of DP on bone were accompanied by a decline in interleukins, TNF and MCP-1, suggesting that DP is acting in part through the immune system to suppress inflammatory activity and reduce the size of the osteoclast precursor pool. Feeding DP was accompanied by an increase in plasma phenolics, some of which have been shown to stimulate bone accrual. In growing and young adult mice DP at levels as low as 5% of diet (w/w) increased bone volume. At higher levels (DP 25%), bone volume was increased by as much as 94%. These data demonstrate that DP feeding dramatically increases peak bone mass during growth.

Dried plum diet protects from bone loss caused by ionizing radiation

Bone loss caused by ionizing radiation is a potential health concern for radiotherapy patients, radiation workers and astronauts. In animal studies, exposure to ionizing radiation increases oxidative damage in skeletal tissues, and results in an imbalance in bone remodeling initiated by increased bone-resorbing osteoclasts. Therefore, we evaluated various candidate interventions with antioxidant or anti-inflammatory activities (antioxidant cocktail, dihydrolipoic acid, ibuprofen, dried plum) both for their ability to blunt the expression of resorption-related genes in marrow cells after irradiation with either gamma rays (photons, 2 Gy) or simulated space radiation (protons and heavy ions, 1 Gy) and to prevent bone loss. Dried plum was most effective in reducing the expression of genes related to bone resorption (Nfe2l2, Rankl, Mcp1, Opg, TNF-α) and also preventing later cancellous bone decrements caused by irradiation with either photons or heavy ions. Thus, dietary supplementation with DP may prevent the skeletal effects of radiation exposures either in space or on Earth.

Osteoporosis in men: findings from the Osteoporotic Fractures in Men Study (MrOS)

The lifespan of men is increasing and this is associated with an increased prevalence of osteoporosis in men. Osteoporosis increases the risk of bone fracture. Fractures are associated with increased disability and mortality, and public health problems. We review here the study of osteoporosis in men as obtained from a longitudinal cohort of community-based older men, the Osteoporotic Fractures in Men Study (MrOS).

Ionizing Radiation Stimulates Expression of Pro-Osteoclastogenic Genes in Marrow and Skeletal Tissue

Exposure to ionizing radiation can cause rapid mineral loss and increase bone-resorbing osteoclasts within metabolically active, cancellous bone tissue leading to structural deficits. To better understand mechanisms involved in rapid, radiation-induced bone loss, we determined the influence of total body irradiation on expression of select cytokines known both to stimulate osteoclastogenesis and contribute to inflammatory bone disease. Adult (16 week), male C57BL/6J mice were exposed to either 2 Gy gamma rays ((137)Cs, 0.8 Gy/min) or heavy ions ((56)Fe, 600MeV, 0.50-1.1 Gy/min); this dose corresponds to either a single fraction of radiotherapy (typical total dose is ≥10 Gy) or accumulates over long-duration interplanetary missions. Serum, marrow, and mineralized tissue were harvested 4 h-7 days later. Gamma irradiation caused a prompt (2.6-fold within 4 h) and persistent (peaking at 4.1-fold within 1 day) rise in the expression of the obligate osteoclastogenic cytokine, receptor activator of nuclear factor kappa-B ligand (Rankl), within marrow cells over controls. Similarly, Rankl expression peaked in marrow cells within 3 days of iron exposure (9.2-fold). Changes in Rankl expression induced by gamma irradiation preceded and overlapped with a rise in expression of other pro-osteoclastic cytokines in marrow (eg, monocyte chemotactic protein-1 increased by 11.9-fold, and tumor necrosis factor-alpha increased by 1.7-fold over controls). The ratio, Rankl/Opg, in marrow increased by 1.8-fold, a net pro-resorption balance. In the marrow, expression of the antioxidant transcription factor, Nfe2l2, strongly correlated with expression levels of Nfatc1, Csf1, Tnf, and Rankl. Radiation exposure increased a serum marker of bone resorption (tartrate-resistant acid phosphatase) and led to cancellous bone loss (16% decrement after 1 week). We conclude that total body irradiation (gamma or heavy-ion) caused temporal elevations in the concentrations of specific genes expressed within marrow and mineralized tissue related to bone resorption, including select cytokines that lead to osteoclastogenesis and elevated resorption; this is likely to account for rapid and progressive deterioration of cancellous microarchitecture following exposure to ionizing radiation.

A novel mouse model of trauma induced heterotopic ossification

Severe soft tissue trauma is associated with heterotopic ossification (HO), the abnormal deposition of bone at extra-skeletal sites. The pathophysiology of the development of trauma-induced HO remains largely unknown due in part to the lack of appropriate animal models. In this study, we sought to develop a new trauma-induced HO mouse model using muscle impact injury combined with low dose BMP-2. BMP-2 at doses ranging from 0 to 2 µg was injected into quadriceps muscles of adult male C57/BL6 mice. Animals then received a one-time quadriceps impaction injury to mimic the trauma associated with severe injuries. HO was monitored using in vivo microCT scanning at 1, 2, 4, and 8 weeks after treatment. After trauma, the expression of BMP-2, -4, BMP receptor 1, SOX9 and RUNX2 were increased in muscle. Although little or no HO was observed in mice receiving 1 µg BMP-2, combining this dose with muscle trauma produced an abundance of HO. At higher doses of BMP-2, trauma did not augment mineral deposition. These results suggest that BMP-2 signaling can sensitize muscle to trauma-induced HO. They also provide the basis for a new model to study the pathogenesis of trauma-induced HO.

CXCL12/CXCR4 signaling in the osteoblast regulates the mesenchymal stem cell and osteoclast lineage populations

The chemokine CXCL12 and its receptor CXCR4 play a key role in regulation of hematopoietic stem cells and cell migratory function during morphogenesis. Osteoblasts express both the ligand and the receptor, but little is known about the role of CXCL12-CXCR4 signaling in maintaining skeletal homeostasis. Using Cre-Lox technology to delete CXCR4 in mature osteoblasts in mice, we show here a significant decrease in bone mass and alterations in cancellous bone structure. CXCR4 gene ablation increased the number of colony-forming units (CFU), CFU-positive for alkaline phosphatase (CFU-AP(+)), and mineralizing nodules in bone marrow stromal cell (BMSC) cultures. The adipocyte precursor population decreased in BMSCs harvested from the KO animals. The nonadherent population of BMSCs harvested from the long bone diaphysis of KO animals formed more osteoclasts, a finding that was associated with increased circulatory levels of pyridinoline, a marker of bone resorption. Our data show that osteoblast-specific CXCR4 deletion has profound effects on the mesenchymal stem cell pool and allocation to the osteoblastic and adipocytic cell lineages. They also show that CXCL12/CXCR4 signaling in the mature osteoblast can feedback to regulate the osteoclast precursor pool size and play a multifunctional role in regulating bone formation and resorption.

Prolonged alendronate treatment prevents the decline in serum TGF-β1 levels and reduces cortical bone strength in long-term estrogen deficiency rat model

INTRODUCTION

While the anti-resorptive effects of the bisphosphonates (BPs) are well documented, many questions remain about their mechanisms of action, particularly following long-term use. This study evaluated the effects of alendronate (Ale) treatment on TGF-β1 signaling in mesenchymal stem cells (MSCs) and osteocytes, and the relationship between prolonged alendronate treatment on systemic TGF-β1 levels and bone strength.

METHODS

TGF-β1 expression and signaling were evaluated in MSCs and osteocytic MLO-Y4 cells following Ale treatment. Serum total TGF-β1 levels, a bone resorption marker (DPD/Cr), three-dimensional microCT scans and biomechanical tests from both the trabecular and cortical bone were measured in ovariectomized rats that either received continuous Ale treatment for 360 days or Ale treatment for 120 days followed by 240 days of vehicle. Linear regression tests were performed to determine the association of serum total TGF-β1 levels and both the trabecular (vertebrae) and cortical (tibiae) bone strength.

RESULTS

Ale increased TGF-β1 signaling in the MSCs but not in the MLO-Y4 cells. Ale treatment increased serum TGF-β1 levels and the numbers of TGF-β1-positive osteocytes and periosteal cells in cortical bone. Serum TGF-β1 levels were not associated with vertebral maximum load and strength but was negatively associated with cortical bone maximum load and ultimate strength.

CONCLUSIONS

The increase of serum TGF-β1 levels during acute phase of estrogen deficiency is likely due to increased osteoclast-mediated release of matrix-derived latent TGF-β1. Long-term estrogen-deficiency generally results in a decline in serum TGF-β1 levels that are maintained by Ale treatment. Measuring serum total TGF-β1 levels may help to determine cortical bone quality following alendronate treatment.

Simulated spaceflight produces a rapid and sustained loss of osteoprogenitors and an acute but transitory rise of osteoclast precursors in two genetic strains of mice

Loss of skeletal weight bearing or skeletal unloading as occurs during spaceflight inhibits bone formation and stimulates bone resorption. These are associated with a decline in the osteoblast (Ob.S/BS) and an increase in the osteoclast (Oc.S/BS) bone surfaces. To determine the temporal relationship between changes in the bone cells and their marrow precursor pools during sustained unloading, and whether genetic background influences these relationships, we used the hindlimb unloading model to induce bone loss in two strains of mice known to respond to load and having significantly different cancellous bone volumes (C57BL/6 and DBA/2 male mice). Skeletal unloading caused a progressive decline in bone volume that was accompanied by strain-specific changes in Ob.S/BS and Oc.S/BS. These were associated with a sustained reduction in the osteoprogenitor population and a dramatic but transient increase in the osteoclast precursor pool size in both strains. The results reveal that bone adaptation to skeletal unloading involves similar rapid changes in the osteoblast and osteoclast progenitor populations in both strains of mice but striking differences in Oc.S/BS dynamics, BFR, and cancellous bone structure. These strain-specific differences suggest that genetics plays an important role in determining the osteoblast and osteoclast populations on the bone surface and the dynamics of bone loss in response to skeletal unloading.

Early response of bone marrow osteoprogenitors to skeletal unloading and sclerostin antibody

Sclerostin functions as an antagonist to Wnt signaling and inhibits bone-forming activity. We studied the effects of skeletal unloading and treatment with sclerostin antibody (Scl-Ab) on mesenchymal stem cell, osteoprogenitor and osteoclast precursor pools, and their relationship to bone formation and resorption. Male C57BL/6 mice (5-months-old) were hind limb unloaded for 1 week or allowed normal ambulation and treated with Scl-Ab (25 mg/kg, s.c. injections on days 1 and 4) or placebo. Unloading decreased the serum concentration of bone formation marker P1NP (-35 %), number of colony-forming units (CFU) (-38 %), alkaline phosphatase-positive CFUs (CFU-AP+) (-51 %), and calcified nodules (-35 %); and resulted in a fourfold increase in the number of osteoclast precursors. The effects of Scl-Ab treatment on unloaded and normally loaded mice were nearly identical; Scl-Ab increased serum P1NP and the number of CFU, CFU-AP+, and calcified nodules in ex vivo cultures; and increased osteoblast and bone mineralizing surfaces in vivo. Although the marrow-derived osteoclast precursor population increased with Scl-Ab, the bone osteoclast surface did not change, and the serum concentration of osteoclast activity marker TRACP5b decreased. Our data suggest that short-term Scl-Ab treatment can prevent the decrease in osteoprogenitor population associated with skeletal unloading and increase osteoblast surface and bone mineralizing surface in unloaded animals. The anabolic effects of Scl-Ab treatment on bone are preserved during skeletal unloading. These findings suggest that Scl-Ab treatment can both increase bone formation and decrease bone resorption, and provide a new means for prevention and treatment of disuse osteoporosis.

Bone turnover markers in peripheral blood and marrow plasma reflect trabecular bone loss but not endocortical expansion in aging mice

We examined age-related changes in biochemical markers and regulators of osteoblast and osteoclast activity in C57BL/6 mice to assess their utility in explaining age-related changes in bone. Several recently discovered regulators of osteoclasts and osteoblasts were also measured to assess concordance between their systemic levels versus their levels in marrow plasma, to which bone cells are directly exposed. MicroCT of 6-, 12-, and 24-month-old mice indicated an early age-related loss of trabecular bone volume and surface, followed by endocortical bone loss and periosteal expansion. Trabecular bone loss temporally correlated with reductions in biomarkers of bone formation and resorption in both peripheral blood and bone marrow. Endocortical bone loss and periosteal bone gain were not reflected in these protein biomarkers, but were well correlated with increased expression of osteocalcin, rank, tracp5b, and cathepsinK in RNA extracted from cortical bone. While age-related changes in bone turnover markers remained concordant in blood versus marrow, aging led to divergent changes in blood versus marrow for the bone cell regulators RANKL, OPG, sclerostin, DKK1, and serotonin. Bone expression of runx2 and osterix increased progressively with aging and was associated with an increase in the number of osteoprogenitors and osteoclast precursors. In summary, levels of biochemical markers of bone turnover in blood and bone marrow plasma were predictive of an age-related loss of trabecular surfaces in adult C57BL/6 mice, but did not predict gains in cortical surfaces resulting from cortical expansion. Unlike these turnover markers, a panel of bone cell regulatory proteins exhibited divergent age-related changes in marrow versus peripheral blood, suggesting that their circulating levels may not reflect local levels to which osteoclasts and osteoblasts are directly exposed.

Changes in cortical bone response to high-fat diet from adolescence to adulthood in mice

Diabetic obesity is associated with increased fracture risk in adults and adolescents. We find in both adolescent and adult mice dramatically inferior mechanical properties and structural quality of cortical bone, in agreement with the human fracture data, although some aspects of the response to obesity appear to differ by age.

INTRODUCTION

The association of obesity with bone is complex and varies with age. Diabetic obese adolescents and adult humans have increased fracture risk. Prior studies have shown reduced mechanical properties as a result of high-fat diet (HFD) but do not fully address size-independent mechanical properties or structural quality, which are important to understand material behavior.

METHODS

Cortical bone from femurs and tibiae from two age groups of C57BL/6 mice fed either HFD or low-fat diet (LFD) were evaluated for structural and bone turnover changes (SEM and histomorphometry) and tested for bending strength, bending stiffness, and fracture toughness. Leptin, IGF-I, and non-enzymatic glycation measurements were also collected.

RESULTS

In both young and adult mice fed on HFD, femoral strength, stiffness, and toughness are all dramatically lower than controls. Inferior lamellar and osteocyte alignment also point to reduced structural quality in both age groups. Bone size was largely unaffected by HFD, although there was a shift from increasing bone size in obese adolescents to decreasing in adults. IGF-I levels were lower in young obese mice only.

CONCLUSIONS

While the response to obesity of murine cortical bone mass, bone formation, and hormonal changes appear to differ by age, the bone mechanical properties for young and adult groups are similar. In agreement with human fracture trends, adult mice may be similarly susceptible to bone fracture to the young group, although cortical bone in the two age groups responds to diabetic obesity differently.

Glucocorticoid dose determines osteocyte cell fate

In response to cellular insult, several pathways can be activated, including necrosis, apoptosis, and autophagy. Because glucocorticoids (GCs) have been shown to induce both osteocyte apoptosis and autophagy, we sought to determine whether osteocyte cell fate in the presence of GCs was dose dependent by performing in vivo and in vitro studies. Male Swiss-Webster mice were treated with slow-release prednisolone pellets at 1.4, 2.8, and 5.6 mg/kg/d for 28 d. An osteocyte cell line, MLO-Y4 cells, was treated with various doses of dexamethasone. We found that GC treatments dose dependently decreased activation of antioxidant-, autophagy-, and antiapoptosis-focused RT-PCR gene pathways in mouse cortical bone. The activation of antioxidant genes was correlated with autophagy gene expression after the GC treatments. The presence of osteocyte autophagy, as detected by immunostaining for LC3, increased ∼50% at the distal femur cortical bone region but not at trabecular bone region at the 1.4 and 2.8 mg/kg/d GC dose levels. The number of apoptotic osteocytes was increased at the cortical bone region by ∼40% initially observed at the 2.8 mg/kg/d dose level. In addition, the presence of the osteocyte autophagy was associated with an increased protein level of cathepsin K in vitro after the GC treatments. In summary, we found that GC treatment dose-dependently decreased antioxidant gene expression, with lower GC doses activating autophagy, whereas a higher dose increased apoptosis. These data suggest that autophagy may provide a mechanism for osteocytes to survive the stress after GC exposure and provide further insight into how GCs alter bone cell fate.

Differential maintenance of cortical and cancellous bone strength following discontinuation of bone-active agents

Osteoporotic patients treated with antiresorptive or anabolic agents experience an increase in bone mass and a reduction in incident fractures. However, the effects of these medications on bone quality and strength after a prolonged discontinuation of treatment are not known. We evaluated these effects in an osteoporotic rat model. Six-month-old ovariectomized (OVX) rats were treated with placebo, alendronate (ALN, 2 µg/kg), parathyroid hormone [PTH(1-34); 20 µg/kg], or raloxifene (RAL, 2 mg/kg) three times a week for 4 months and withdrawn from the treatments for 8 months. Treatment with ALN, PTH, and RAL increased the vertebral trabecular bone volume (BV/TV) by 47%, 53%, and 31%, with corresponding increases in vertebral compression load by 27%, 51%, and 31%, respectively (p < .001). The resulting bone strength was similar to that of the sham-OVX control group with ALN and RAL and higher (p < .001) with PTH treatment. After 4 months of withdrawal, bone turnover (BFR/BS) remained suppressed in the ALN group versus the OVX controls (p < .001). The vertebral strength was higher than in the OVX group only in ALN-treated group (p < .05), whereas only the PTH-treated animals showed a higher maximum load in tibial bending versus the OVX controls (p < .05). The vertebral BV/TV returned to the OVX group level in both the PTH and RAL groups 4 months after withdrawal but remained 25% higher than the OVX controls up to 8 months after withdrawal of ALN (p < .05). Interestingly, cortical bone mineral density increased only with PTH treatment (p < .05) but was not different among the experimental groups after withdrawal. At 8 months after treatment withdrawal, none of the treatment groups was different from the OVX control group for cortical or cancellous bone strength. In summary, both ALN and PTH maintained bone strength (maximum load) 4 months after discontinuation of treatment despite changes in bone mass and bone turnover; however, PTH maintained cortical bone strength, whereas ALN maintained cancellous bone strength. Additional studies on the long-term effects on bone strength after discontinuation and with combination of osteoporosis medications are needed to improve our treatment of osteoporosis.

Inhibition of the progesterone nuclear receptor during the bone linear growth phase increases peak bone mass in female mice

Augmentation of the peak bone mass (PBM) may be one of the most effective interventions to reduce the risk of developing osteoporosis later in life; however treatments to augment PBM are currently limited. Our study evaluated whether a greater PBM could be achieved either in the progesterone nuclear receptor knockout mice (PRKO) or by using a nuclear progesterone receptor (nPR) antagonist, RU486 in mice. Compared to their wild type (WT) littermates the female PRKO mice developed significantly higher cancellous and cortical mass in the distal femurs, and this was associated with increased bone formation. The high bone mass phenotype was partially reproduced by administering RU486 in female WT mice from 1–3 months of age. Our results suggest that the inhibition of the nPR during the rapid bone growth period (1–3 months) increases osteogenesis, which results in acquisition of higher bone mass. Our findings suggest a crucial role for progesterone signaling in bone acquisition and inhibition of the nPR as a novel approach to augment bone mass, which may have the potential to reduce the burden of osteoporosis.

Higher doses of bisphosphonates further improve bone mass, architecture, and strength but not the tissue material properties in aged rats

We report the results of a series of experiments designed to determine the effects of ibandronate (Ibn) and risedronate (Ris) on a number of bone quality parameters in aged osteopenic rats to explain how bone material and bone mass may be affected by the dose of bisphosphonates (BP) and contribute to their anti-fracture efficacy. Eighteen-month old female rats underwent either ovariectomy or sham surgery. The ovariectomized (OVX) groups were left untreated for 2 months to develop osteopenia. Treatments started at 20 months of age as follows: sham and OVX control (treated with saline), OVX + risedronate 30 and 90 (30 or 90 microg/kg/dose), and OVX + ibandronate 30 and 90 (30 or 90 microg/kg/dose). The treatments were given monthly for 4 months by subcutaneous injection. At sacrifice at 24 months of age the 4th lumbar vertebra was used for microCT scans (bone mass, architecture, and degree of mineralization of bone, DMB) and histomorphometry, and the 6th lumbar vertebra, tibia, and femur were collected for biomechanical testing to determine bone structural and material strength, cortical fracture toughness, and tissue elastic modulus. The compression testing of the vertebral bodies (LVB6) was simulated using finite-element analysis (FEA) to also estimate the bone structural stiffness. Both Ibn and Ris dose-dependently increased bone mass and improved vertebral bone microarchitecture and mechanical properties compared to OVX control. Estimates of vertebral maximum stress from FEA were correlated with vertebral maximum load (r=0.5, p<0.001) and maximum stress (r=0.4, p<0.005) measured experimentally. Tibial bone bending modulus and cortical strength increased compared to OVX with both BP but no dose-dependent effect was observed. DMB and elastic modulus of trabecular bone were improved with Ibn 30 compared to OVX but were not affected in other BP-treated groups. DMB of tibial cortical bone showed no change with BP treatments. The fracture toughness examined in midshaft femurs did not change with BP even with the higher doses. In summary, the anti-fracture efficacy of BP is largely due to their preservation of bone mass and while the higher doses further improve the bone structural properties do not improve the localized bone material characteristics such as tissue strength, elastic modulus, and cortical toughness.

Cross-calibration of 45calcium kinetics against dynamic histomorphometry in a rat model to determine bone turnover

Techniques for assessing bone dynamic are in high demand. Calcium (Ca) kinetic studies are currently being used in our clinical studies of bone turnover in adolescents and elderly. The technique has rarely been compared to the standard method of bone dynamic histomorphometry. We perturbed bone turnover through ovariectomy and sub-optimal dietary Ca in a female rat model to cross-calibrate Ca kinetics against dynamic histomorphometry. Kinetic studies involved oral and intravenous administration of (45)Ca and monitoring the tracer in blood, urine, feces, and bone over a 3-day period as part of a metabolic Ca balance study. Histomorphometric indices of mineral apposition rate, mineralizing surface, and bone formation rate were obtained from proximal metaphysis and mid-diaphysis region of tibial bone. Bone mineralization and resorption rates at the whole skeletal level as evaluated by kinetic studies were significantly correlated with the volume-based bone formation rate (BFR/BV) evaluated by dynamic histomorphometry in metaphyseal trabecular bone (r=0.72 and r=0.61, respectively, p<0.001) and surface-based bone formation rate (BFR/BS) in tibial cortex (r=0.63, p<0.001 and r=0.59, p<0.01, respectively). Significant correlations were also demonstrated between bone resorption and mineralization rates at the whole skeletal level (r=0.91, p<0.001) using (45)Ca kinetic data. Ca kinetic modeling showed an increase (p<0.001) in skeletal resorption and formation rates in response to ovariectomy (27.6 vs. 13.8 mg/d for bone resorption and 42.7 vs. 28 mg/d for bone formation in ovariectomized vs. their Sham-operated control animals, respectively). Ca kinetic data also showed that bone formation decreased by 30% and whole bone balance by 50%, when dietary Ca level was reduced from 0.4% to 0.2% (34.2 vs. 23.8 mg/d and 10.4 vs. 5.1 mg/d, respectively, p<0.001). Our data suggest that Ca kinetic studies can be used reliably to rapidly detect changes in bone turnover at the whole skeletal level in response to interventions.

Effect of paricalcitol and cinacalcet on serum phosphate, FGF-23, and bone in rats with chronic kidney disease

Calcimimetics activate the calcium-sensing receptor (CaR) and reduce parathyroid hormone (PTH) by increasing the sensitivity of the parathyroid CaR to ambient calcium. The calcimimetic, cinacalcet, is effective in treating secondary hyperparathyroidism in dialysis patients [chronic kidney disease (CKD 5)], but little is known about its effects on stage 3-4 CKD patients. We compared cinacalcet and paricalcitol in uremic rats with creatinine clearances "equivalent" to patients with CKD 3-4. Uremia was induced in anesthetized rats using the 5/6th nephrectomy model. Groups were 1) uremic control, 2) uremic + cinacalcet (U+Cin; 15 mg x kg(-1) x day(-1) po for 6 wk), 3) uremic + paricalcitol (U+Par; 0.16 microg/kg, 3 x wk, ip for 6 wk), and 4) normal. Unlike U+Par animals, cinacalcet promoted hypocalcemia and marked hyperphosphatemia. The Ca x P in U+Cin rats was twice that of U+Par rats. Both compounds suppressed PTH. Serum 1,25-(OH)(2)D(3) was decreased in both U+Par and U+Cin rats. Serum FGF-23 was increased in U+Par but not in U+Cin, where it tended to decrease. Analysis of tibiae showed that U+Cin, but not U+Par, rats had reduced bone volume. U+Cin rats had similar bone formation and reduced osteoid surface, but higher bone resorption. Hypocalcemia, hyperphosphatemia, low 1,25-(OH)(2)D(3), and cinacalcet itself may play a role in the detrimental effects on bone seen in U+Cin rats. This requires further investigation. In conclusion, due to its effects on bone and to the hypocalcemia and severe hyperphosphatemia it induces, we believe that cinacalcet should not be used in patients with CKD without further detailed studies.

Overexpression of secreted frizzled-related protein 1 inhibits bone formation and attenuates parathyroid hormone bone anabolic effects

Secreted frizzled-related protein 1 (sFRP1) is an antagonist of Wnt signaling, an important pathway in maintaining bone homeostasis. In this study we evaluated the skeletal phenotype of mice overexpressing sFRP1 (sFRP1 Tg) and the interaction of parathyroid hormone (PTH) treatment and sFRP1 (over)expression. Bone mass and microarchitecture were measured by micro-computed tomography (microCT). Osteoblastic and osteoclastic cell maturation and function were assessed in primary bone marrow cell cultures. Bone turnover was assessed by biochemical markers and dynamic bone histomorphometry. Real-time PCR was used to monitor the expression of several genes that regulate osteoblast maturation and function in whole bone. We found that trabecular bone mass measurements in distal femurs and lumbar vertebral bodies were 22% and 51% lower in female and 9% and 33% lower in male sFRP1 Tg mice, respectively, compared with wild-type (WT) controls at 3 months of age. Genes associated with osteoblast maturation and function, serum bone formation markers, and surface based bone formation were significantly decreased in sFRP1 Tg mice of both sexes. Bone resorption was similar between sFRP1 Tg and WT females and was higher in sFRP1 Tg male mice. Treatment with hPTH(1-34) (40 microg/kg/d) for 2 weeks increased trabecular bone volume in WT mice (females: +30% to 50%; males: +35% to 150%) compared with sFRP1 Tg mice (females: +5%; males: +18% to 54%). Percentage increases in bone formation also were lower in PTH-treated sFRP1 Tg mice compared with PTH-treated WT mice. In conclusion, overexpression of sFRP1 inhibited bone formation as well as attenuated PTH anabolic action on bone. The gender differences in the bone phenotype of the sFRP1 Tg animal warrants further investigation.

Supplemental dietary racemic equol has modest benefits to bone but has mild uterotropic activity in ovariectomized rats

Soy isoflavones and their metabolites, with estrogenic activity, have been considered candidates for reducing postmenopausal bone loss. In this study, we examined the effect of dietary equol, a bioactive metabolite of the soy isoflavone daidzein, on equol tissue distribution, bone parameters, and reproductive tissue activity using an adult ovariectomized (OVX) rat model. An 8-wk feeding study was conducted to compare 4 dietary treatments of equol (0, 50, 100, 200 mg/kg diet) in 6-mo-old OVX female Sprague-Dawley rats. A dose response increase in tissue equol concentrations was observed for serum, liver, kidney, and heart, and a plateau occurred at 100 mg equol/kg diet for intestine. In OVX rats receiving 200 mg equol/kg diet, femoral calcium concentration was greater than those receiving lower doses but was still less than SHAM (P < 0.05), and other bone measures were not improved. Tibia calcium concentrations were lower in OVX rats receiving 100 and 200 mg equol/kg diet compared with the OVX control rats. Trabecular bone mineral density of tibia was also lower in equol-fed OVX rats. At this dietary equol intake, uterine weight was higher (P < 0.05) than in other OVX groups but lower than the SHAM-operated intact rats. The 200 mg/kg diet dose of dietary equol significantly increased proliferative index in the uterine epithelium. Dietary equol had no stimulatory effect on mammary gland epithelium. We conclude that in OVX rats, a dietary equol dose that had modest effect on bone also exerts mild uterotropic effects.

Diet calcium level but not calcium supplement particle size affects bone density and mechanical properties in ovariectomized rats

Calcium (Ca) supplements, especially Ca carbonate (CaCO3), are the main alternative sources of dietary Ca and an important part of a treatment regimen for osteoporosis, the most common metabolic bone disorder of aging and menopause. In a female ovariectomized (OVX) rat model for studying postmenopausal osteoporosis, we tested the hypothesis that a small compared with a large particle size of CaCO3 (13.0- vs. 18.5-mum geometric diameter) would result in increased Ca balance and subsequently bone mass and that this would be affected by dietary Ca level. We used 6-mo-old rats that were OVX either at 6 or 3 mo of age as models of early or stable menopausal status, respectively. The rats received semipurified diets that contained either 0.4 or 0.2% dietary Ca provided from CaCO3 of 2 particle sizes. A group of Sham-operated rats with intact ovaries served as control and were fed 0.4% dietary Ca from large particles. Estrogen deficiency as a result of ovariectomy had an adverse effect on bone density, mineral content, and bone mechanical properties (P < 0.001). Reducing dietary Ca from 0.4 to 0.2% resulted in significant adverse effects on bone density and mechanical properties (P < 0.001). The particle size of CaCO3 did not affect total Ca balance, bone dual energy X-ray absorptiometry and peripheral quantitative computed tomography indices, bone ash and Ca content, or the mechanical determinants of bone strength. We conclude that a decrease in particle size of CaCO3 to 70% of that typically found in Ca supplements does not provide a benefit to overall Ca metabolism or bone characteristics and that the amount of Ca consumed is of greater influence in enhancing Ca nutrition and skeletal strength.

Targeting the Wnt signaling pathway to augment bone formation

Recent discoveries in humans and mice have revealed that the Wnt (Wingless and Int-1) signaling pathway is responsible for a complex array of functions in maintaining bone homeostasis. The Wnt proteins are key modulators of mesenchymal lineage specification and regulate most aspects of osteoblast physiology and postnatal bone acquisition by controlling the differentiation and activity of osteoblasts and osteoclasts. Initial reports have indicated that activators of Wnt signaling are potent promoters of osteogenesis; however, systemic hyperactivation of the canonical Wnt pathway could potentially accelerate neoplastic transformation and subsequent tumor growth. Alternatively, recent investigations of natural soluble antagonists of Wnt signaling in bone suggest the possibilities of bone-specific therapies targeting the negative regulators of Wnt pathway, especially sclerostin. With this new knowledge, novel pharmacologic interventions that alter Wnt signaling are being evaluated for the management of osteoporosis. In this article, we briefly describe the Wnt signaling elements, their characterized role in bone, and summarize the current knowledge on the potential to enhance bone formation through the manipulation of Wnt signaling antagonists.

Strontium administration in young chickens improves bone volume and architecture but does not enhance bone structural and material strength

Genetic selection for rapid body growth in broiler chickens has resulted in adverse effects on the skeletal system exemplified by a higher rate of cortical fractures in leg bones. Strontium (Sr) has been reported to have beneficial effects on bone formation and strength. We supplemented the diet of 300-day-old chicks with increasing dosages of Sr (0%, 0.12%, or 0.24%) to study the capacity of the element to improve bone quality and mechanical integrity. Treatment with Sr increased cortical bone volume and reduced bone porosity as measured by micro-computed tomography. The higher level of Sr significantly reduced bone Ca content (34.7%) relative to controls (37.2%), suggesting that Sr replaced some of the Ca in bone. Material properties determined by the three-point bending test showed that bone in the Sr-treated groups withstood greater deformation prior to fracture. Load to failure and ultimate stress were similar across groups. Our results indicate that Sr treatment in rapidly growing chickens induced positive effects on bone volume but did not improve the breaking strength of long bones.

Effects of strontium on bone strength, density, volume, and microarchitecture in laying hens

Strontium has been reported to have beneficial effects on bone. Treatment of laying hens, which are susceptible to osteoporosis and bone fracture, with strontium increased DXA measurements of BMD and BMC and microCT measurements of bone volume and microarchitecture and improved the mechanical performance of whole bone, but had no effect on the estimated material properties of the bone tissue.

INTRODUCTION

Strontium (Sr) has been reported to dissociate bone remodeling and have positive influences on bone formation. We supplemented the diet of laying hens, which are susceptible to osteoporosis and bone fracture, with Sr to study the capacity of the element to improve bone mechanical integrity and resistance to fracture.

MATERIALS AND METHODS

Increasing dosages of Sr (0, 3000, 4500, and 6000 ppm) were fed to 196 13-week-old pullets for 11 months. BMD and BMC, as measured by conventional and DXA methods, microarchitectural parameters derived from microCT, and structural and material properties as determined by three-point bending test, were studied. Calcium (Ca), phosphorus (P), and Sr levels in plasma and bone, as well as egg output, shell quality, and composition, were assessed.

RESULTS

Sr concentrations in plasma and bone increased in a dose-dependent manner without affecting Ca and P. Treatment with Sr increased BMD and BMC as measured by DXA, increased cortical and medullary bone volume, trabecular thickness, number, and surface, and improved whole bone ultimate load, but had no effect on the estimated material properties of diaphyseal bone. Sr also increased the ash content of eggshells and did not affect egg output and shell quality.

CONCLUSIONS

Sr supplementation induced large positive effects on bone density, volume, and microarchitecture as measured by radiographic methods. Sr treatment also improved the structural strength of diaphyseal bone but had no effect on the estimated material properties of the bone tissue.