Augment Bone Mass Research Articles

Gulp1 deficiency augments bone mass in malemice by affecting osteoclasts due to elevated 17β-estradiol levels.

The engulfment adaptor phosphotyrosine-binding domain containing 1 (GULP1) is an adaptor protein involved in the engulfment of apoptotic cells via phagocytosis. Gulp1 was first found to promote the phagocytosis of apoptotic cells by macrophages, and its role in various tissues, including neurons and ovaries, has been well studied. However, the expression and function of GULP1 in bone tissue are poorly understood. Consequently, to determine whether GULP1 plays a role in the regulation of bone remodeling in vitro and in vivo, we generated Gulp1 knockout (KO) mice. Gulp1 was expressed in bone tissue, mainly in osteoblasts, while its expression is very low in osteoclasts. Microcomputed tomography and histomorphometry analysis in 8-week-old male Gulp1 KO mice revealed a high bone mass in comparison with male wild-type (WT) mice. This was a result of decreased osteoclast differentiation and function in vivo and in vitro as confirmed by a reduced actin ring and microtubule formation in osteoclasts. Gas chromatography-mass spectrometry analysis further showed that both 17β-estradiol (E2) and 2-hydroxyestradiol levels, and the E2/testosterone metabolic ratio, reflecting aromatase activity, were also higher in the bone marrow of male Gulp1 KO mice than in male WT mice. Consistent with mass spectrometry analysis, aromatase enzymatic activity was significantly higher in the bone marrow of male Gulp1 KO mice. Altogether, our results suggest that GULP1 deficiency decreases the differentiation and function of osteoclasts themselves and increases sex steroid hormone-mediated inhibition of osteoclast differentiation and function, rather than affecting osteoblasts, resulting in a high bone mass in male mice. To the best of our knowledge, this is the first study to explore the direct and indirect roles of GULP1 in bone remodeling, providing new insights into its regulation.

Urinary Metabolic Profiling via LC-MS/MS Reveals Impact of Bovine Lactoferrin on Bone Formation in Growing SD Rats.

Lactoferrin (LF) exerts a promoting bone health function. The effects of LF on bone formation at the metabolic level have been less explored. Urinary metabolic profiling of growing Sprague-Dawley (SD) rats LF-supplemented (1000 mg/kg bw) for four weeks were explored by Liquid chromatography–tandem mass spectrometry (LC-MS/MS). The serum markers of bone formation and bone resorption, the bone mass, and the osteogenesis markers of femur were measured by an enzyme-linked immunosorbent assay, micro-computerized tomography, and immunohistochemistry, respectively. Compared with the control, LF supplementation improved bone formation (p < 0.05), reduced bone resorption (p < 0.05), enhanced femoral bone mineral density and microarchitecture (p < 0.05), and upregulated osteocalcin, osterix, and Runx-2 expression (p < 0.05) of femur. LF upregulated 69 urinary metabolites. KEGG and pathway enrichment analyses of those urinary metabolites, and the Person’s correlation analyses among those urinary metabolites and bone status revealed that LF impacted on bone formation via regulatory comprehensive pathways including taurine and hypotaurine metabolism, arginine and proline metabolism, cyanoamino acid metabolism, nitrogen metabolism, nicotinate and nicotinamide metabolism, and fatty acid biosynthesis. The present study indicated the metabolomics is a useful and practical tool to elucidate the mechanisms by which LF augments bone mass formation in growing animals.

Gallium and silicon synergistically promote osseointegration of dental implant in patients with osteoporosis

Over the last few decades, a wide variety of dental implants have been successfully placed in jaw bones to restore tooth function. But major challenges still remain in patients with osteoporosis involving compromised osseointegration, and the therapeutic methods is far from optimism. Gallium can directly inhibit bone osteolysis, prevent bone calcium release and augment bone mass, which makes Ga unique among the potential antiresorptive drugs. Silicon, as an indispensable modulator in bone formation, presents its bone anabolic effects, while reduces, at least doesn’t increase, bone resorption. We hypothesize that the combination of bone anabolic effects of Si and antiresorptive effects of Ga will result in synergistic effects on the improvement of osteointegration under osteoporotic condition. In our strategy, in order to maximize the efficacy while minimize the side effects of ions, a novel titania mesoporous layer fabricated by electrochemical anodization on the surface of titanium implant will be employed as a promising local drug delivery system. The synergistic effects of Ga and Si on improving osseointegration will be verified by animal experiments, and be furthered by clinical trials. Our hypothesis could help to create an option to improve success rate of dental implants in osteoporotic patients.

Orexin Regulates Bone Remodeling via a Dominant Positive Central Action and a Subordinate Negative Peripheral Action

Orexin neuropeptides promote arousal, appetite, reward, and energy expenditure. However, whether orexin affects bone mass accrual is unknown. Here, we show that orexin functions centrally through orexin receptor 2 (OX2R) in the brain to enhance bone formation. OX2R null mice exhibit low bone mass owing to elevated circulating leptin, whereas central administration of an OX2R-selective agonist augments bone mass. Conversely, orexin also functions peripherally through orexin receptor 1 (OX1R) in the bone to suppress bone formation. OX1R null mice exhibit high bone mass owing to a differentiation shift from marrow adipocyte to osteoblast that results from higher osseous ghrelin expression. The central action is dominant because bone mass is reduced in orexin null and OX1R2R double null mice but enhanced in orexin-overexpressing transgenic mice. These findings reveal orexin as a critical rheostat of skeletal homeostasis that exerts a yin-yang dual regulation and highlight orexin as a therapeutic target for osteoporosis.

Local injection of a single dose of simvastatin augments osteoporotic bone mass in ovariectomized rats

The aim of this study was to evaluate the effects and explore the mechanism of a local injection of a single dose of simvastatin as a strategy to strengthen target bone. Simvastatin was injected into the femurs (5 or 10 mg) or caudal vertebrae (1 or 2 mg) of ovariectomized rats, with an equal volume of vehicle injected as a control. Bone mineral density (BMD), bone microstructure and strength were evaluated at 1 and 5 months post-injection for the femurs and at 12 days post-injection for the vertebrae. Bone mass, adipocyte numbers and Runx2 expression were also examined using histology and immunohistochemistry. Compared with controls, simvastatin significantly increased BMD, bone volume fraction (BV/TV), improved bone microstructural parameters and bone strength in the femurs at both time points (all P < 0.01). Simvastatin-treated femurs contained fewer adipocytes and a higher Runx2 expression. For the caudal vertebrae, simvastatin significantly improved BV/TV, bone microstructures, and bone strength (all P < 0.01) as compared with controls. In conclusion, local injection of a single dose of simvastatin induces early onset and long-lasting bone augmentation in osteoporotic bone, significantly improving BMD, and bone microstructure and biomechanical strength. Simvastatin induces Runx2 expression, which may function to induce osteogenesis and inhibit adipogenesis as an underlying mechanism to augment bone mass.

Whole-Body Vibration During Passive Standing in Individuals With Spinal Cord Injury: Effects of Plate Choice, Frequency, Amplitude, and Subject's Posture on Vibration Propagation

To date, few pharmacologic or rehabilitation interventions for sublesional osteoporosis (SLOP) or low bone mass of the hip and knee regions after spinal cord injury (SCI) have produced significant or sustained increases in lower extremity bone mineral density. Whole body vibration (WBV) is a potential intervention for the prevention and/or treatment of SLOP. To identify the optimal WBV conditions (ie, plate, frequency, amplitude, and subject posture) among men with chronic SCI during passive standing and facilitate the implementation and future evaluation of the efficacy of WBV and passive standing for prevention and treatment of SLOP in men with SCI. This phase 0 device development study assessed the lower extremity propagation characteristics of WBV in men with and without SCI by using a variety of a priori specified plates, frequencies, amplitudes, and postures that facilitate lower extremity vibration absorption while minimizing vibration propagation to the head. A tertiary SCI rehabilitation center in Toronto, Canada. Healthy men with chronic paraplegia (n = 5) and those without SCI (n = 7), ages 20-50 years, weight 68-113 kg, and height 168-188 cm. An EasyStand standing frame (Altimate Medical Inc, Morton, MN) was fitted onto 2 commercially available vibration platforms: WAVE (WAVE Manufacturing Inc, Windsor, Ontario, Canada) and Juvent (Juvent Medical Inc, Somerset, NJ). Accelerometers were attached to the participants' forehead, hip, knee, and ankle to measure vibration propagation. Vibration parameters evaluated were posture (knee angles of 140°, 160°, and 180° [180° for Juvent only]), vibration frequency (25 Hz, 35 Hz, and 45 Hz), and vibration amplitude (0.6 mm and 1.2 mm [WAVE only]). The subjects were exposed to all combinations of posture, frequencies, and amplitudes during the experiments (total parameter combinations: 12 WAVE and 9 Juvent). Peak-to-peak vibration and transmissibility of vibration were recorded and computed for each accelerometer at the tested locations. Variations in frequency generated the most noticeable changes in propagation characteristics, followed by variations in knee angle and amplitude. WBV therapy delivered with use of the WAVE platform with a knee angle of 140°, plate frequency of 45 Hz, and amplitude of 1.2 mm met our a priori criteria for the "optimal WBV condition." Future studies should evaluate the therapeutic efficacy of the WAVE platform by using these parameters to maintain or augment bone mass among persons with SCI and SLOP.

ZP2307, a novel, cyclic PTH(1-17) analog that augments bone mass in ovariectomized rats

Daily injections of human parathyroid hormone (1-34), hPTH(1-34), provide a highly effective treatment option for severe osteoporosis. However, PTH analogs shorter than 28 amino acids do not retain any bone augmenting potential. Here, we present ZP2307 ([Ac₅c¹, Aib³, Leu⁸, Gln¹⁰, Har¹¹, Ala¹², Trp¹⁴, Asp¹⁷]PTH(1-17)-NH₂), a novel, chemically modified and cyclized hPTH(1-17) analog, that augments bone mass in ovariectomized, osteopenic rats. Subcutaneous administration of this structurally constrained, K¹³-D¹⁷ side-chain-to-side-chain cyclized peptide reversed bone loss and increased bone mineral density (BMD) up to or above baseline levels in rat long bones and vertebrae. Highly significant effects of ZP2307 were achieved at doses of 40-320 nmol/kg. Micro-CT and histomorphometric analyses showed that ZP2307 improved quantitative and qualitative parameters of bone structure. Biomechanical testing of rat femora confirmed that ZP2307 dramatically increased bone strength. Over a broad maximally effective dose range (40-160 nmol/kg) ZP2307 did not increase serum concentrations of ionized free calcium above normal levels. Only at the highest dose (320 nmol/kg) ZP2307 induced hypercalcemic calcium levels in the ovariectomized rats. To our knowledge ZP2307 is the smallest PTH peptide analog known to exert augmentation of bone. Our findings suggest that ZP2307 has the potential to effectively augment bone mass over a broad dose range without a concomitant increase in the serum concentration of ionized free calcium above the normal range.

Rescuing loading induced bone formation at senescence.

The increasing incidence of osteoporosis worldwide requires anabolic treatments that are safe, effective, and, critically, inexpensive given the prevailing overburdened health care systems. While vigorous skeletal loading is anabolic and holds promise, deficits in mechanotransduction accrued with age markedly diminish the efficacy of readily complied, exercise-based strategies to combat osteoporosis in the elderly. Our approach to explore and counteract these age-related deficits was guided by cellular signaling patterns across hierarchical scales and by the insight that cell responses initiated during transient, rare events hold potential to exert high-fidelity control over temporally and spatially distant tissue adaptation. Here, we present an agent-based model of real-time Ca2+/NFAT signaling amongst bone cells that fully described periosteal bone formation induced by a wide variety of loading stimuli in young and aged animals. The model predicted age-related pathway alterations underlying the diminished bone formation at senescence, and hence identified critical deficits that were promising targets for therapy. Based upon model predictions, we implemented an in vivo intervention and show for the first time that supplementing mechanical stimuli with low-dose Cyclosporin A can completely rescue loading induced bone formation in the senescent skeleton. These pre-clinical data provide the rationale to consider this approved pharmaceutical alongside mild physical exercise as an inexpensive, yet potent therapy to augment bone mass in the elderly. Our analyses suggested that real-time cellular signaling strongly influences downstream bone adaptation to mechanical stimuli, and quantification of these otherwise inaccessible, transient events in silico yielded a novel intervention with clinical potential.

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.

Effects of low-magnitude, high-frequency mechanical stimulation in the rat osteopenia model

SummaryIn this study, short-term, whole-body vertical vibration at 90 Hz improved trabecular bone quality. There was an improvement of bone quality and density in both osteoporotic and control rats. This treatment may therefore be an attractive option for the treatment of osteoporosis.IntroductionAside from pharmacological treatment options, physical exercise is known to augment bone mass. In this study, the effects of whole-body vertical vibration (WBVV) on bone quality and density were evaluated using an osteoporotic rat model.MethodsSixty female Sprague Dawley rats were ovariectomized (C) or sham (SHAM) operated at the age of 3 months. After 3 months, both groups were divided into two subgroups that received either WBVV at 90 Hz for 35 days or no treatment. After sacrificing the rats, we evaluated vertebral bone strength, histomorphometric parameters, and bone mineral density (BMD).ResultsTreatment with WBVV resulted in improved biomechanical properties. The yield load after WBVV was significantly enhanced. According to yield load and Young’s modulus, the treated OVX rats reached the level of the untreated SHAM animals. In all measured histomorphometric parameters, WBVV significantly improved bone density. Treatment with WBVV demonstrated greater effects on the trabecular bone compared to the cortical bone. The ash-BMD index showed significant differences between treated and untreated rats.ConclusionUsing WBVV as a non-pharmacological supportive treatment option for osteoporosis demonstrated an enhancement of bone strength and bone mass. This procedure may be an attractive option for the treatment of osteoporosis.

Alfacalcidol treatment increases bone mass from anticatabolic and anabolic effects on cancellous and cortical bone in intact female rats

It has been reported that alfacalcidol had an anticatabolic and anabolic effect on bone in ovariectomized and aged male rat models, but this has not been tested on intact female rats. The current study was to determine the effects of alfacalcidol on cancellous and cortical bone in intact female rats with or without exercise. Seventy-four, 8.5-month-old, intact female rats were orally treated with 0, 0.005, 0.025, 0.05, or 0.1 microg/kg alfacalcidol alone or in combination with raised cage (RC) exercise for 3 months. In vivo peripheral quantitative computerized tomography (pQCT) of the proximal tibial metaphyses (PTM) and ex vivo histomorphometric analyses of the PTM and tibial shaft (TX) were performed. Only the 0.1 microg alfacalcidol/kg dose proved to be anabolic. pQCT analysis showed that this dose increased total and cortical bone mineral content and density and trabecular bone mineral density. Histomorphometrically, it induced an anabolic response by increased trabecular mass and microarchitecture from stimulated cancellous bone and bone bouton formations, and suppressed bone resorption more than bone formation on the trabecular and endocortical surfaces, to produce a positive bone balance. A positive correlation between trabecular connectivity and bone bouton numbers occurred. These findings suggest alfacalcidol treatment augments bone mass by increased cancellous bone mass and improved trabecular architecture through its anticatabolic and anabolic properties in the intact adult female rat. Last, raised cage exercise alone or the combination of raised cage and alfacalcidol was no more effective than alfacalcidol alone.

Prostaglandin E2 receptors in bone formation

Prostaglandins, PGE(2) in particular, have diverse actions on various organs, including inflammation, bone healing, bone formation, embryo implantation, induction of labour and vasodilatation, among others. However, systemic side effects have limited their clinical utility. The pharmacological activities of PGE(2) are mediated through four G protein-coupled receptor subtypes, EP1-EP4. Recent studies have shown that EP2 and EP4 receptors play important roles in regulating bone formation and resorption. EP2 and EP4 receptor-selective agonists have been shown to stimulate local or systemic bone formation, augment bone mass and accelerate the healing of fractures or bone defects in animal models upon local or systemic administration, thus, potentially offering new therapeutic options for enhancing bone formation and bone repair in humans. This review will focus on the studies related to bone formation and bone healing in the EP receptor knockout (KO) mice and the EP2 or EP4 receptor-selective agonist treated animal models.

Evidências da ação de agentes físicos sobre o metabolismo do tecido ósseo e seus potenciais usos clínicos

The action of physical agents such as low level laser therapy, low-intensity pulsed ultrasound and electrical and electromagnetic fields on bone have been often studied, showing that they are able to promote osteogenesis, accelerate fracture consolidation and augment bone mass. The use of these therapeutic modalities was first based on the finding that bone is a piezoelectric material, that means it can generate polarization when deformed, transforming mechanical energy into electric energy, and this has widen therapeutic possibilities to bony tissue. The present work aims to present evidences of physiologic effects and mechanisms of action of these physical agents on bone metabolism, based on articles published in international scientific literature.

Parathyroid Hormone Secretion and Action: Evidence for Discrete Receptors for the Carboxyl-Terminal Region and Related Biological Actions of Carboxyl-Terminal Ligands

PTH is a major systemic regulator of the concentrations of calcium, phosphate, and active vitamin D metabolites in blood and of cellular activity in bone. Intermittently administered PTH and amino-terminal PTH peptide fragments or analogs also augment bone mass and currently are being introduced into clinical practice as therapies for osteoporosis. The amino-terminal region of PTH is known to be both necessary and sufficient for full activity at PTH/PTHrP receptors (PTH1Rs), which mediate the classical biological actions of the hormone. It is well known that multiple carboxyl-terminal fragments of PTH are present in blood, where they comprise the major form(s) of circulating hormone, but these fragments have long been regarded as inert by-products of PTH metabolism because they neither bind to nor activate PTH1Rs. New in vitro and in vivo evidence, together with older observations extending over the past 20 yr, now points strongly to the existence of novel large carboxyl-terminal PTH fragments in blood and to receptors for these fragments that appear to mediate unique biological actions in bone. This review traces the development of this field in the context of the evolution of our understanding of the "classical" receptor for amino-terminal PTH and the now convincing evidence for these receptors for carboxyl-terminal PTH. The review summarizes current knowledge of the structure, secretion, and metabolism of PTH and its circulating fragments, details available information concerning the pharmacology and actions of carboxyl-terminal PTH receptors, and frames their likely biological and clinical significance. It seems likely that physiological parathyroid regulation of calcium and bone metabolism may involve receptors for circulating carboxy-terminal PTH ligands as well as the action of amino-terminal determinants within the PTH molecule on the classical PTH1R.

Obesity during childhood and adolescence augments bone mass and bone dimensions

Studies of the effect of childhood obesity on bone accrual during growth have yielded conflicting results, largely related to the failure to adequately characterize the confounding effects of growth, maturation, and body composition. The objective of this study was to determine the effect of childhood obesity on skeletal mass and dimensions relative to height, body composition, and maturation in males and females. In 132 nonobese (body mass index < 85th percentile) and 103 obese (body mass index > or = 95th percentile) subjects aged 4-20 y, whole-body and vertebral bone mineral content (BMC) was determined by using dual-energy X-ray absorptiometry, and bone area, areal bone mineral density (BMD), and fat and lean masses were measured. Vertebral volumetric BMD was estimated as BMC/area(1.5). Obesity was associated with greater height-for-age, advanced maturation for age, and greater lean mass for height (all P < 0.001). Sex-specific multivariate regressions with adjustment for maturation showed that obesity was associated with greater vertebral areal BMD for height, greater volumetric BMD, and greater vertebral BMC for bone area (all P < 0.05). After adjustment for maturation and lean mass, obesity was associated with significantly greater whole-body bone area and BMC for age and for height (all P < 0.001). In contrast with the results of prior studies, obesity during childhood and adolescence was associated with increased vertebral bone density and increased whole-body bone dimensions and mass. These differences persisted after adjustment for obesity-related increases in height, maturation, and lean mass. Future studies are needed to determine the effect of these differences on fracture risk.

Les nouveaux traitements ostéoformateurs de l'ostéoporose

Purpose. – Antiresorptive therapy are usual treatment of osteoporosis, but they prevent no more than 40 or 60% of osteoporotic fracture. Thus, there is a need for osteoformative agents that can further augment bone mass and reduce risk fracture more substantially. Current knowledger and keypoints. – Daily injections of 1–34 aminoterminal fragment of PTH increase bone formation and bone mass. A randomized study recently demonstrated that PTH 1–34 decrease the risk of vertebral and non vertebral fracture, and the place of this treatment in the strategy of osteoporosis treatment is to demonstrate. Oral administration of strontium salt at low dosage level stimulate bone formation and decrease bone resorption. Preliminary data needs to be confirmed by a multicenter antifracture study. Retrospective results with statins in three international studies have not be confirmed by the only randomized clinical trial. Use of low dose intermittent fluoride therapy are still recommanded by some authors. Futures prospects and projects. – Effects of insuline like growth factor I and other growing factor on bone turnover have to be confirmed in human, and pharmacological and tolerance problems have to be solved.

Systemic prostaglandin E2 increases cancellous bone formation and mass in aging rats and stimulates their bone marrow osteogenic capacity in vivo and in vitro.

Prostaglandin E(2) (PGE(2)) has been shown to exert a bone anabolic effect in young and adult rats. In this study we tested whether it possesses a similar effect on bone formation and bone mass in aging rats. Fifteen-month-old rats were injected daily with either PGE(2) at 5 mg/kg or vehicle for 14 days. PGE(2) treatment stimulated the rate of cancellous bone formation (a approximately 5.5-fold increase in bone formation rate), measured by the incorporation of calcein into bone-forming surfaces at the tibial proximal metaphysis. This effect resulted in increased cancellous bone area (+54%) at the same site. Since PGE(2) treatment resulted in a much higher proportion of bone surface undergoing bone formation and thus lined with osteoblasts, we tested the hypothesis that PGE(2) stimulates osteoblast differentiation from bone marrow precursor cells both in vivo and in vitro. We found that ex vivo cultures of bone marrow stromal cells from rats injected for 2 weeks with PGE(2) at 5 mg/kg per day yielded more ( approximately 4-fold) mineralized nodules and exhibited a greater (by 30-40%) alkaline phosphatase activity compared with cultures from vehicle-injected rats, attesting to a stimulation of osteoblastic differentiation by PGE(2). We also compared the osteogenic capacity of bone marrow from aging (15-month-old) versus young (5-week-old) rats and its regulation by PGE(2) in vitro. Bone marrow stromal cell cultures from aging rats exhibited a greatly diminished osteogenic capacity, reflected in reduced nodule formation ( approximately 6% of young animals) and lower alkaline phosphatase activity ( approximately 60% of young animals). However, these parameters could be stimulated in both groups of animals by incubation with 10-100 nM PGE(2). The magnitude of this stimulation was greater in cultures from aging rats (+550% vs +70% in nodule formation of aging compared with young rats). In conclusion, we demonstrate here that PGE(2) exerts a bone anabolic effect in aging rats, similar to the effect we and others have reported in young, growing rats. The PGE(2)-stimulated bone formation, which augments bone mass, most likely results from recruitment of osteoblasts from their bone marrow stromal precursors.

Bone mass increases in less than 4 wk of voluntary exercising in growing rats.

Physical exercise is known to augment bone mass, but the specific mechanisms by which physical activity influences skeletal metabolism is still not thoroughly understood. So far, time related events of bone tissue adaptation to physical training have not been investigated. We, therefore, studied the time-course effects of daily spontaneous exercise training on bone metabolism in the rat by biochemical and tissue analyses. Forty-five 4-wk-old female Dark Agouti rats were used, randomly assigned to voluntary exercising groups of five animals for 1, 2, 3, and 4 wk, or to age-matched sedentary controls. At sacrifice, blood was sampled for determination of parameters of bone and calcium metabolism (osteocalcin, alkaline phosphatases, total and ionized calcium, phosphorus, parathyroid hormone). Right and left tibiae were removed for bone mass (dry and ash mass, mineral content) and histomorphometric analyses. We found that the animals performed large amounts of exercise (reaching 50 +/- 8 km x wk(-1)), and that this voluntary physical training induced significant changes in bone metabolism. An increase (approximately 32%) in serum alkaline phosphatase activity was already measurable at the end of the first week of exercising and persisted throughout the experiment, accompanied by a concomitant increase in osteoblastic bone formation (approximately 27%), as evaluated in bone tissue. These changes were associated with consecutive increases in tibial bone mass (approximately 7.6%), mineral content (approximately 7.4%) and metaphyseal bone volume (approximately 17%) measurable 4 wk after the onset of exercise, with interesting positive correlations between tibial bone mass parameters and soleus muscle mass. Conversely, no change was evidenced in biochemical parameters of calcium metabolism, except for an increase in phosphorus serum levels in trained animals. Daily spontaneous exercise training induced an increase in bone mass and bone volume in less than 4 wk. Further studies are needed to fully investigate these changes during the very first days of exercising.

Differential effects of systemic prostaglandin E2 on bone mass in rat long bones and calvariae.

Prostaglandin E2 (PGE2) has been shown to possess anabolic properties when administered systemically. All the experiments performed so far examined long bones from animals of varying age and bone status. In this study we compared the changes in bone mass of long bones (femur, tibia and humerus) to those in calvariae after a 3-week daily administration of 6 mg/kg PGE2 into 3-week-old rats. This regimen inhibited body weight gain (by 14.1%) as well as longitudinal growth of long bones (by 2.2-3.5%) but increased their mass. Ash weight (measuring both cancellous and compact bone) increased by 10.1-14.1% but tibial cancellous bone area was elevated by 54%. Radial growth was slightly reduced due to transient inhibition of mineral apposition rate at the periosteal envelope but the expansion of the marrow cavity was inhibited to a greater extent, resulting in an 8.1% increase in the relative compact bone area. The increased bone mass was associated with greater mechanical strength of the femoral neck (24.2% increase in fracture load and 19% in stiffness). In contrast, PGE2 administration did not affect calvarial thickness or mineral apposition rate but increased its density, i.e. reduced the area of marrow spaces due to stimulation of endocortical bone formation at this site. The pattern of bone mass changes documented in this study closely correlates with that of the induced expression of early-response genes following a single dose of PGE2 as we recently reported. These data, therefore, support the hypothesis that in vivo administration of an anabolic dose of PGE2 increases bone formation and augments bone mass largely by stimulating the recruitment of new osteoblasts via induction of the proliferation and/or differentiation of bone marrow osteogenic precursors.

Gallium nitrate increases type I collagen and fibronectin mRNA and collagen protein levels in bone and fibroblast cells

Gallium is a Group IIIa transitional element with therapeutic efficacy in the treatment of metabolic bone disorders. Previously described antiresorptive effects of gallium on osteoclasts are not sufficient to account for the full range of effects of gallium on bone structure and metabolism. We have recently shown that gallium nitrate inhibits osteocalcin gene expression and the synthesis of osteocalcin protein, an osteoblast-specific bone matrix protein that is thought to serve as a signal to trigger osteoclastic resorption. Here we present evidence for an additional mechanism by which gallium may function to augment bone mass by altering matrix protein synthesis by osteoblastic and fibroblastic cells. Rat calvarial explants exposed to gallium nitrate for 48 h showed increased incorporation of 3H-proline into hydroxyproline and collagenase digestible protein. In addition, gallium treatment increased steady-state mRNA levels for fibronectin and type I procollagen chains in primary rat calvarial osteoblast-enriched cultures, the ROS 17/2.8 osteoblastic osteosarcoma line, and nontransformed human dermal fibroblasts. These findings suggest that the exposure of mesenchymally-derived cells to gallium results in an altered pattern of matrix protein synthesis that would favor increased bone formation.