Treatment with growth hormone and IGF-I in growing rats increases bone mineral content but not bone mineral density

Pharmaceutical treatment of bone loss: From animal models and drug development to future treatment strategies

Animal models are fundamental to advance our knowledge of the underlying pathophysiology of bone loss and to study pharmaceutical countermeasures against it. The animal model of post-menopausal osteoporosis from ovariectomy is the most widely used preclinical approach to study skeletal deterioration. However, several other animal models exist, each with unique characteristics such as bone loss from disuse, lactation, glucocorticoid excess, or exposure to hypobaric hypoxia. The present review aimed to provide a comprehensive overview of these animal models to emphasize the importance and significance of investigating bone loss and pharmaceutical countermeasures from perspectives other than post-menopausal osteoporosis only. Hence, the pathophysiology and underlying cellular mechanisms involved in the various types of bone loss are different, and this might influence which prevention and treatment strategies are the most effective. In addition, the review sought to map the current landscape of pharmaceutical countermeasures against osteoporosis with an emphasis on how drug development has changed from being driven by clinical observations and enhancement or repurposing of existing drugs to today's use of targeted anti-bodies that are the result of advanced insights into the underlying molecular mechanisms of bone formation and resorption. Moreover, new treatment combinations or repurposing opportunities of already approved drugs with a focus on dabigatran, parathyroid hormone and abaloparatide, growth hormone, inhibitors of the activin signaling pathway, acetazolamide, zoledronate, and romosozumab are discussed. Despite the considerable progress in drug development, there is still a clear need to improve treatment strategies and develop new pharmaceuticals against various types of osteoporosis. The review also highlights that new treatment indications should be explored using multiple animal models of bone loss in order to ensure a broad representation of different types of skeletal deterioration instead of mainly focusing on primary osteoporosis from post-menopausal estrogen deficiency.

Alpha-Ketoglutarate as a Molecule with Pleiotropic Activity: Well-Known and Novel Possibilities of Therapeutic Use

Alpha-ketoglutarate (AKG), an endogenous intermediary metabolite in the Krebs cycle, is a molecule involved in multiple metabolic and cellular pathways. It functions as an energy donor, a precursor in the amino acid biosynthesis, a signalling molecule, as well as a regulator of epigenetic processes and cellular signalling via protein binding. AKG is an obligatory co-substrate for 2-oxoglutarate-dependent dioxygenases, which catalyse hydroxylation reactions on various types of substrates. It regulates the activity of prolyl-4 hydroxylase, which controls the biosynthesis of collagen, a component of bone tissue. AKG also affects the functioning of prolyl hydroxylases, which, in turn, influences the function of the hypoxia-inducible factor, an important transcription factor in cancer development and progression. Additionally, it affects the functioning of enzymes that influence epigenetic modifications of chromatin: ten-eleven translocation hydroxylases involved in DNA demethylation and the Jumonji C domain containing lysine demethylases, which are the major histone demethylases. Thus, it regulates gene expression. The metabolic and extrametabolic function of AKG in cells and the organism open many different fields for therapeutic interventions for treatment of diseases. This review presents the results of studies conducted with the use of AKG in states of protein deficiency and oxidative stress conditions. It also discusses current knowledge about AKG as an immunomodulatory agent and a bone anabolic factor. Additionally, the regulatory role of AKG and its structural analogues in carcinogenesis as well as the results of studies of AKG as an anticancer agent are discussed.

Use of Animal Models in Understanding Cancer-induced Bone Pain

Many common cancers have a propensity to metastasize to bone. Although malignancies often go undetected in their native tissues, bone metastases produce excruciating pain that severely compromises patient quality of life. Cancer-induced bone pain (CIBP) is poorly managed with existing medications, and its multifaceted etiology remains to be fully elucidated. Novel analgesic targets arise as more is learned about this complex and distinct pain state. Over the past two decades, multiple animal models have been developed to study CIBP’s unique pathology and identify therapeutic targets. Here, we review animal models of CIBP and the mechanistic insights gained as these models evolve. Findings from immunocompromised and immunocompetent host systems are discussed separately to highlight the effect of model choice on outcome. Gaining an understanding of the unique neuromolecular profile of cancer pain through the use of appropriate animal models will aid in the development of more effective therapeutics for CIBP.

Excessive growth hormone expression in male GH transgenic mice adversely alters bone architecture and mechanical strength

Patients with acromegaly have a higher prevalence of vertebral fractures despite normal bone mineral density (BMD), suggesting that GH overexpression has adverse effects on skeletal architecture and strength. We used giant bovine GH (bGH) transgenic mice to analyze the effects of high serum GH levels on BMD, architecture, and mechanical strength. Five-month-old hemizygous male bGH mice were compared with age- and sex-matched nontransgenic littermates controls (NT; n=16/group). Bone architecture and BMD were analyzed in tibia and lumbar vertebrae using microcomputed tomography. Femora were tested to failure using three-point bending and bone cellular activity determined by bone histomorphometry. bGH transgenic mice displayed significant increases in body weight and bone lengths. bGH tibia showed decreases in trabecular bone volume fraction, thickness, and number compared with NT ones, whereas trabecular pattern factor and structure model index were significantly increased, indicating deterioration in bone structure. Although cortical tissue perimeter was increased in transgenic mice, cortical thickness was reduced. bGH mice showed similar trabecular BMD but reduced trabecular thickness in lumbar vertebra relative to controls. Cortical BMD and thickness were significantly reduced in bGH lumbar vertebra. Mechanical testing of femora confirmed that bGH femora have decreased intrinsic mechanical properties compared with NT ones. Bone turnover is increased in favor of bone resorption in bGH tibia and vertebra compared with controls, and serum PTH levels is also enhanced in bGH mice. These data collectively suggest that high serum GH levels negatively affect bone architecture and quality at multiple skeletal sites.

Combined treatment with GH and IGF-I: additive effect on cortical bone mass but not on linear bone growth in female rats

The growth-promoting effect of combined therapy with GH and IGF-I in normal rats is not known. We therefore investigated the efficacy of treatment with recombinant human (rh)GH and/or rhIGF-I on longitudinal bone growth and bone mass in intact, prepubertal, female Sprague-Dawley rats. rhGH was injected twice daily sc (5 mg/kg·d) and rhIGF-I continuously infused sc (2.2 or 4.4 mg/kg·d) for 28 days. Longitudinal bone growth was monitored by weekly x-rays of tibiae and nose-anus length measurements, and tibial growth plate histomorphology was analyzed. Bone mass was evaluated by peripheral quantitative computed tomography. In addition, serum levels of IGF-I, rat GH, acid labile subunit, IGF binding protein-3, 150-kDa ternary complex formation, and markers of bone formation and degradation were measured. Monotherapy with rhGH was more effective than rhIGF-I (4.4 mg/kg·d) to increase tibia and nose-anus length, whereas combined therapy did not further increase tibia, or nose-anus, lengths or growth plate height. In contrast, combined rhGH and rhIGF-I (4.4 mg/kg·d) therapy had an additive stimulatory effect on cortical bone mass vs rhGH alone. Combined treatment with rhGH and rhIGF-I resulted in markedly higher serum IGF-I concentrations vs rhGH alone but did not compromise the endogenous secretion of GH. We conclude that rhIGF-I treatment augments cortical bone mass but does not further improve bone growth in rhGH-treated young, intact, female rats.

Gender-dependence of bone structure and properties in adult osteogenesis imperfecta murine model

Osteogenesis imperfecta (OI) is a dominant skeletal disorder characterized by bone fragility and deformities. Though the oim mouse model has been the most widely studied of the OI models, it has only recently been suggested to exhibit gender-dependent differences in bone mineralization. To characterize the impact of gender on the morphometry/ultra-structure, mechanical properties, and biochemical composition of oim bone on the congenic C57BL/J6 background, 4-month-old oim/oim, +/oim, and wild-type (wt) female and male tibiae were evaluated using micro-computed tomography, three-point bending, and Raman spectroscopy. Dramatic gender differences were evident in both cortical and trabecular bone morphological and geometric parameters. Male mice had inherently more bone and increased moment of inertia than genotype-matched female counterparts with corresponding increases in bone biomechanical strength. The primary influence of gender was structure/geometry in bone growth and mechanical properties, whereas the mineral/matrix composition and hydroxyproline content of bone were influenced primarily by the oim collagen mutation. This study provides evidence of the importance of gender in the evaluation and interpretation of potential therapeutic strategies when using mouse models of OI.

Insulin-like growth factor-1 increases bone calcium accumulation only during rapid growth in female rats

Calcium retention varies with developmental state, which may be partially under the control of insulin-like growth factor 1 (IGF-1). IGF-1 levels can be manipulated through dietary and therapeutic interventions. We investigated the relationship between IGF-1 endogenous production and calcium utilization and bone accretion during growth as well as the effects of IGF-1 treatment on calcium utilization during rapid and slowed growth in intact female Sprague-Dawley rats. In 33 rats killed at 11 time points (n = 3 each) from age 4 to 24 wk, femoral and vertebral bone mass were paralleled by plasma IGF-1 up to 9 wk. Fractional calcium absorption was maximal at 9 wk, reduced by one-half at 12 wk, and there was no further change at 20 wk. From this study, we selected 2 stages of growth, rapid and slow, for a subsequent intervention study. A 4-wk intervention was initiated at 6 or 8 wk when rats (n = 15/group) received either continuous rhIGF-1/IGF binding protein 3 (IGFBP3) infusion (0.3 mg/d) or vehicle (control) by osmotic mini-pumps. In rapidly growing IGF-1/IGFBP3-treated rats compared to controls, but not in slowly growing treated compared to control rats, IGF-1 treatment increased (P < 0.05) calcium absorption (35 vs. 21%), bone calcium balance (0.55 vs. 0.3 mmol/d), and femoral calcium content (31 vs. 24% of dry weight). Exogenous IGF-1/IGFBP3 treatment increased calcium accretion during rapid growth, but rats past rapid growth were no longer as sensitive to this dose of IGF-1/IGFBP3. Thus, interventions designed to improve bone mass through increased IGF-1 will have the greatest impact during rapid growth.

Differential effects on proliferation of GH and IGFs in sea bream (Sparus aurata) cultured myocytes

Primary culture of gilthead sea bream skeletal muscle cells was used to examine the effects of growth hormone (GH) and insulin-like growth factors (IGFs) in fish muscle proliferation and growth. Proliferation was measured as the percentage of positive cells expressing the proliferating cell nuclear antigen (PCNA) analyzed by immunocytochemistry. First, the effects of GH from two different origins (mammals and fish) were tested. GH from human (hGH) did not stimulate proliferation except at 3h at the dose of 1 nM. On the other hand, sea bream GH (sbGH) significantly stimulated proliferation, without differences between the three incubation times studied (3, 6, and 18 h), at the dose of 10nM, demonstrating that the homologous hormone has a more potent effect. In addition, the results with the IGFs indicated that both peptides, IGF-I and IGF-II significantly stimulated proliferation of sea bream myocytes, but IGF-II showed higher effects than IGF-I, and even than those of sbGH. Finally, the combinations of peptide treatments (GHs with IGFs) indicated that IGF-I has higher effects on proliferation when it is combined with GHs compared with IGF-I alone, while IGF-II has similar effects alone or combined with either GH. These results indicate that IGF-II may have an important role on muscle proliferation that appears to be independent of GH. On the contrary, IGF-I seems to play a synergistic action with GH stimulating myocyte proliferation.

Periodontal disease in adults with untreated congenital growth hormone deficiency: a case-control study

AIM

The aim of this study was to investigate the possible associations between isolated growth hormone deficiency (IGHD) and periodontal attachment loss (PAL) in adults affected by congenital IGHD.

MATERIALS AND METHODS

Forty-five previously identified IGHD subjects were eligible for this study. The final study sample comprised 32 cases (gender:20M/12F; age:44.8 ± 17.5) matched for age, gender, diabetes, smoking status and income to 32 controls (non-IGHD subjects). Participants were submitted to a full-mouth clinical examination of six sites per tooth and were interviewed using a structured, written questionnaire. Periodontitis was defined as proximal PAL≥5 mm affecting ≥30% of teeth.

RESULTS

No significant differences were observed in the percentage of sites with visible plaque between IGHD and non-IGHD subjects (59.4% versus 46.9%, p=0.32). IGHD subjects had significant less supragingival calculus (31.3% versus 59.4%, p=0.02) and more bleeding on probing (71.9% versus 18.8%, p<0.01) than controls. PAL≥5 mm was significantly more prevalent (100% versus 71.9%, p<0.01) and affected more teeth (30.5% versus 6.7%, p<0.01) in cases than in controls. After adjusting for supragingival calculus, IGHD cases had a higher likelihood of having periodontitis than controls (OR=17.4-17.8, 95% CI=2.3-134.9, p=0.004-0.005).

CONCLUSION

Congenital IGHD subjects have a greater chance of having PAL.

Administration of growth hormone in selectively protein-deprived rats decreases BMD and bone strength

INTRODUCTION

Isocaloric protein undernutrition is associated with decreased bone mass and decreased bone strength, together with lower IGF-I levels. It remains unclear whether administration of growth hormone (GH) corrects these alterations in bone metabolism.

MATERIALS AND METHODS

Six-month-old female rats were fed isocaloric diets containing either 2.5% or 15% casein for 2 weeks. Bovine growth hormone (bGH, 0.5 or 2.5mg/kg of body weight) or vehicle was then administered as subcutaneous injections, twice daily, to rats on either diet for 4 weeks. At the proximal tibia, analysis of bone mineral density (BMD), maximal load and histomorphometry were performed. In addition, urinary deoxypyridinoline, plasma osteocalcin and IGF-I concentrations were measured. Weight was monitored weekly.

RESULTS

bGH caused a dose-dependent increase in plasma IGF-I regardless of the dietary protein content. However, bGH dose-dependently decreased BMD and bone strength in rats fed the low-protein diet. There was no significant effect of bGH on BMD in rats fed the normal protein diet within this short-term treatment period, however bone formation as detected by histomorphometry was improved in this group but not the low-protein group. Osteoclast surface was increased in the low-protein bGH-treated animals only. Changes in bone turnover markers were detectable under both normal and low-protein diets.

CONCLUSION

These results emphasize the major importance of dietary protein intake in the bone response to short-term GH administration, and highlight the need for further investigation into the effects of GH treatment in patients with reduced protein intake.

BMP-6 and mesenchymal stem cell differentiation

Bone morphogenetic protein-6 (BMP-6) is produced by bone marrow-mesenchymal (BMSC) and hematopoietic stem cells, which can differentiate into bone, cartilage, adipose, muscle, hematopoietic, synovial and other tissues. Bmp6-/- null mice have low hepcidin serum levels and an iron overload, resembling hereditary hemochromatosis, which may cause a reduced number of pancreatic beta-cells, increased serum glucose and diabetes. BMP-6 circulates in the normal human plasma and is produced by BMSC prior to differentiation into osteoblasts. Moreover, it is also released by osteoclasts as a key bone coupling factor recruiting osteoblasts to the resorption site. Due to unique structural, receptor binding and signaling characteristics much smaller amounts of BMP-6 than BMP-7 are needed in vivo to induce regeneration of bone defects in animals.

The relationship between the GH/IGF-I axis and serum markers of bone turnover metabolism in healthy children

CONTEXT

There is evidence to suggest that IGF-I plays a role in regulating bone turnover.

OBJECTIVE

To evaluate the relationships between serum concentrations of IGF-I and IGF-binding protein-3 (IGFBP-3), and bone metabolism markers in healthy children.

DESIGN AND SETTING

Prospective cross-sectional study.

SUBJECTS AND METHODS

A cohort of 579 boys and 540 girls, all healthy Caucasian, were included in this study. Serum IGF-I and IGFBP-3 concentrations, bone alkaline phosphatase (BAP) and CrossLaps (markers of bone formation and bone resorption respectively) levels were evaluated as a function of age, gender, pubertal stage and body mass index.

RESULTS

Serum IGF-I SDS levels were positively correlated with BAP and CrossLaps SDS levels before and after puberty, and also with CrossLaps during puberty (weak correlation). Serum IGFBP-3 SDS levels were positively correlated with BAP and CrossLaps levels before, during (weak correlation) and after puberty (for BAP levels only).

CONCLUSIONS

This study demonstrated the independent association between serum IGF-I and IGFBP-3 concentrations with both serum bone formation and resorption markers in healthy children. Physiological differences before, during and after puberty in the association of serum IGF-I and IGFBP-3 levels with the serum bone metabolism markers were found. These differences may be related to differences in interactions between sex steroid hormones and the GH/IGF-I system, bone metabolism and growth during the pubertal transition. Improvements in our understanding of life course determinants of the IGF-I system and bone metabolism are required to shed further light on the role of the GH/IGF-I axis in bone remodelling.

Congenic mice provide in vivo evidence for a genetic locus that modulates serum insulin-like growth factor-I and bone acquisition

We identified quantitative trait loci (QTL) that determined the genetic variance in serum IGF-I through genome-wide scanning of mice derived from C57BL/6J(B6) x C3H/HeJ(C3H) intercrosses. One QTL (Igf1s2), on mouse chromosome 10 (Chr10), produces a 15% increase in serum IGF-I in B6C3 F2 mice carrying c3 alleles at that position. We constructed a congenic mouse, B6.C3H-10 (10T), by backcrossing c3 alleles from this 57-Mb region into B6 for 10 generations. 10T mice have higher serum and skeletal IGF-I, greater trabecular bone volume fraction, more trabeculae, and a higher number of osteoclasts at 16 wk, compared with B6 (P < 0.05). Nested congenic sublines generated from further backcrossing of 10T allowed for recombination and produced four smaller sublines with significantly increased serum IGF-I at 16 wk (i.e. 10-4, 10-7, 10-10, and 10-13), compared with B6 (P < 0.0003), and three smaller sublines that showed no differences in IGF-I vs. age- and gender-matched B6 mice. Like 10T, the 10-4 nested sublines at 16 wk had higher femoral mineral (P < 0.0001) and greater trabecular connectivity density with significantly more trabeculae than B6 (P < 0.01). Thus, by comprehensive phenotyping, we were able to narrow the QTL to an 18.3-Mb region containing approximately 148 genes, including Igf1 and Elk-3(ETS domain protein). Allelic differences in the Igf1s2 QTL produce a phenotype characterized by increased serum IGF-I and greater peak bone density. Congenic mice establish proof of concept of shared genetic determinants for both circulating IGF-I and bone acquisition.

Systemically administered bone morphogenetic protein-6 restores bone in aged ovariectomized rats by increasing bone formation and suppressing bone resorption

Although recombinant human bone morphogenetic proteins (BMPs) are used locally for treating bone defects in humans, their systemic effect on bone augmentation has not been explored. We have previously demonstrated that demineralized bone (DB) from ovariectomized (OVX) rats cannot induce bone formation when implanted ectopically at the subcutaneous site. Here we showed in vitro that 17beta-estradiol (E2) specifically induced expression of Bmp6 mRNA in MC3T3-E1 preosteoblastic cells and that bone extracts from OVX rats lack BMPs. Next we demonstrated that 125I-BMP-6 administered systemically accumulated in the skeleton and also restored the osteoinductive capacity of ectopically implanted DB from OVX rats. BMP-6 applied systemically to aged OVX rats significantly increased bone volume and mechanical characteristics of both the trabecular and cortical bone, the osteoblast surface, serum osteocalcin and osteoprotegerin levels, and decreased the osteoclast surface, serum C-telopeptide, and interleukin-6. E2 was significantly less effective, and was not synergistic with BMP-6. Animals that discontinued BMP-6 therapy maintained bone mineral density gains for another 12 weeks. BMP-6 increased in vivo the bone expression of Acvr-1, Bmpr1b, Smad5, alkaline phosphatase, and collagen type I and decreased expression of Bmp3 and BMP antagonists, chordin and cerberus. These results show, for the first time, that systemically administered BMP-6 restores the bone inductive capacity, microarchitecture, and quality of the skeleton in osteoporotic rats.

Mineral changes in osteoporosis: a review

Bone mineral composition, crystallinity, and bone mineral content of osteoporotic patients are different from those of normal subjects. We review the evidence that these mineralization parameters contribute to the strength (fracture resistance) of bone and the methods that have been used to examine them. A specific example is provided from analysis of biopsies from the Multiple Outcomes in Raloxifene Evaluation trial. For the analyses, randomly selected biopsies from placebo, low-dose, and high-dose groups (n = 5 per group) obtained at time zero and 2 years after treatment were examined by infrared imaging spectroscopy. In all cases, comparable increases in mineral content were found, but there were no significant variations in mineral crystallinity.

Regional distinctions in cortical bone mineral density measured by pQCT can predict alterations in material property at the tibial diaphysis of the Cynomolgus monkey

We examined whether regional differences in cortical bone mineral density (Ct.BMD) measured by peripheral quantitative computed tomography is related to the heterogeneity of bone tissue and whether regional Ct.BMD is a better indicator of changes in bone material properties. Bilateral tibiae were obtained from 17 female adult Cynomolgus monkeys (Macaca fascicularis; mean age 16.8 years). After determining that Ct.BMD was similar between the right and left tibiae, the left tibiae were used for bone histomorphometry and the right for a three-point bending test. The Ct.BMD in the posterior quadrant was significantly higher than that in the anterior quadrant. In the bone histomorphometric analysis, all parameters (i.e., average osteonal area, average osteonal bone area, osteon population density, percent osteonal area [%On.Ar], percent osteonal bone area [%On.B.Ar], percent osteonal area of initial remodeling [%Il.On.Ar], percent osteonal area of secondary remodeling [%Sd.On.Ar], porosity, and percent osteoid area in the posterior region) were significantly lower than those in the anterior region. The results indicated that in the same cross-section, bone tissue structure was heterogeneous. Both total- and posterior-Ct.BMD were positively correlated with breaking stress and negatively correlated with toughness, whereas anterior-Ct.BMD was positively correlated with elastic modulus. Backward stepwise multiple regression analyses indicated that posterior-Ct.BMD and total-Ct.BMD were the best variables for predicting breaking stress and toughness, respectively, when age is taken into account. The %On.Ar, %On.B.Ar, and %Il.On.Ar in the posterior region were negatively correlated with elastic modulus. The %On.Ar, %On.B.Ar, and %Sd.On.Ar in the posterior region were positively correlated with toughness. These findings indicated that regional Ct.BMD measurement is useful to assess changes in the material properties of bone associated with the degree of mineralization. In particular, anterior-, posterior-, and total-Ct.BMD can be used separately to predict changes in the material properties of the tibial diaphysis.

Alpha-ketoglutarate treatment early in postnatal life improves bone density in lambs at slaughter

This study has investigated the long-term effect on skeletal development of a short postnatal period of oral alpha-ketoglutarate (AKG) administration, a compound known to regulate the synthesis of proline, which in turn is important for collagen production. Male lambs born to Shropshire ewes were used in this study. Lambs were randomly assigned to either an AKG-treated group or a control group receiving an equal volume of distilled water. AKG-treated lambs received 0.1 g/kg body weight orally from the first 14 days of postnatal life. Lambs were slaughtered at approximately 130 day of life and a body weight of 43-49 kg. Plasma samples, collected from lambs at days 14 and 130, were analyzed for IGF-1 concentration using sheep-specific RIA kits. Bone development was determined on the femur in terms of geometrical and mechanical properties and quantitative computed tomography (QCT). Trabecular bone density, cortical bone density, and the mechanical properties of the bones were significantly higher for AKG-treated compared with control lambs. However, neither plasma IGF-1 concentration nor the geometrical properties of the bones were significantly influenced by AKG treatment. It is concluded that early postnatal treatment of lambs with AKG positively affects bone strength, an effect that does not appear to be mediated by an increased plasma IGF-1 concentration.

Selective reduction in cortical bone mineral density in turner syndrome independent of ovarian hormone deficiency

Women with Turner syndrome (TS) are at risk for osteoporosis from ovarian failure and possibly from haploinsufficiency for bone-related X-chromosome genes. To establish whether cortical or trabecular bone is predominantly affected, and to control for the ovarian failure, we studied forearm bone mineral density (BMD) in 41 women with TS ages 18-45 yr and in 35 age-matched women with karyotypically normal premature ovarian failure (POF). We measured BMD at the 1/3 distal radius (D-Rad(1/3); predominantly cortical bone) and at the ultradistal radius (UD-Rad; predominantly trabecular bone) by dual x-ray absorptiometry. Women with TS had lower cortical BMD compared with POF (D-Rad(1/3) Z-score = -1.5 +/- 0.8 for TS and 0.08 +/- 0.7 for POF; P < 0.0001). In contrast, the primarily trabecular UD-Rad BMD was normal in TS and not significantly different from POF (Z-score = -0.62 +/- 1.1 for TS and -0.34 +/- 1.0 for POF; P = 0.26). The difference in cortical BMD remained after adjustment for height, age of puberty, lifetime estrogen exposure, and serum 25-hydroxyvitamin D (P = 0.0013). Cortical BMD was independent of serum IGF-I and -II, PTH, and testosterone in TS. We conclude that there is a selective deficiency in forearm cortical bone in TS that appears independent of ovarian hormone exposure and is probably related to X-chromosome gene(s) haploinsufficiency.

Bone density and body composition in children with growth hormone insensitivity syndrome receiving recombinant IGF-I

OBJECTIVE

There are few reports of the metabolic action of insulin-like growth factor 1 (IGF-I) in vivo. Growth hormone insensitivity syndrome is a good model to examine the effects of IGF-I deficiency. This study was designed to assess body composition and bone density in children with growth hormone insensitivity syndrome before and after receiving treatment with recombinant IGF-I.

DESIGN

A prospective longitudinal study.

PATIENTS

Four prepubertal boys age 6.1-9.8 years with short stature due to growth hormone insensitivity syndrome.

MEASUREMENTS

Assessment of body fat by skinfold thickness measurements and dual energy X-ray absorptiometry (DXA) was made during the first 6 months of recombinant IGF-I treatment. Assessment of lumbar spine bone density by DXA was performed prior to IGF-I treatment and during the subsequent five years.

RESULTS

Each child showed a significant reduction in fat mass (0.26-1.22 kg) after 6 weeks of IGF-I treatment. Bone density prior to treatment was reduced in comparison to age-matched controls but calculated volumetric bone density was within the normal range. Volumetric bone density progressively improved over the 5-year treatment period.

CONCLUSIONS

Children with growth hormone insensitivity syndrome exhibit a metabolic response to IGF-I within 6 weeks analogous to that seen in GH-deficient children receiving GH. Bone density when corrected for body size is within normal limits and demonstrates a response to IGF-I, confirming the anabolic action on bone.

Evidence that sensitivity to growth hormone (GH) is growth period and tissue type dependent: studies in GH-deficient lit/lit mice

We previously found that the magnitude of skeletal deficits caused by GH deficiency varied during different growth periods. To test the hypothesis that the sensitivity to GH is growth period dependent, we treated GH-deficient lit/lit mice with GH (4 mg/kg body weight.d) or vehicle during the prepubertal and pubertal (d 7-34), pubertal (d 23-34), postpubertal (d 42-55), and adult (d 204-217) periods and evaluated GH effects on the musculoskeletal system by dual energy x-ray absorptiometry (DEXA) and peripheral quantitative computed tomography. GH treatment during different periods significantly increased total body bone mineral content, bone mineral density (BMD), bone area, and lean body mass and decreased percentage of fat compared with vehicle; however, the magnitude of change varied markedly depending on the treatment period. For example, the increase in total body BMD was significantly (P < 0.01) greater when GH was administered between d 42-55 (15%) compared with pubertal (8%) or adult (7.7%) periods, whereas the net loss in percentage of body fat was greatest (-56%) when GH was administered between d 204 and 216 and least (-27%) when GH was administered between d 7 and 35. To determine whether GH-induced anabolic effects on the musculoskeletal system are maintained after GH withdrawal, we performed DEXA measurements 3-7 wk after stopping GH treatment. The increases in total body bone mineral content, BMD, and lean body mass, but not the decrease in body fat, were sustained after GH withdrawal. Our findings demonstrate that the sensitivity to GH in target tissues is growth period and tissue type dependent and that continuous GH treatment is necessary to maintain body fat loss but not BMD gain during a 3-7 wk follow-up.

Transiently increased bone density after irradiation and the radioprotectant drug amifostine in a rat model

At therapeutic levels in pediatric patients, radiation causes damage to the growth plate and contributes to growth deformity and fractures. The purpose of this project was to examine the effects of x-ray irradiation on regional bone mineral density (BMD) and osteoclast histology of rat bone with and without radioprotectant amifostine (AMF) pretreatment. Seventy-two weanling rats had their right knee irradiated with single fraction 17.5 Gy, whereas the left leg was used as an internal control. Twelve animals were euthanized at each of 6 time periods (0.5-6 wk) after irradiation, half having received 100 mg/kg amifostine. BMD (g/cm3) was determined for both the right and left femurs using peripheral quantitative computed tomography (CT) (pQCT). Tibial sections were stained for osteoclasts/chondroclasts with tartrate-resistant acid phosphatase. Statistically significant increases in BMD within the radiation field were seen in the treatment groups' right irradiated legs over the control unirradiated left legs at all time points from 0.5 through 6 weeks. Anatomically, a peak in BMD occurs in the region immediately adjacent to the chondro-osseous junction at 2 weeks after irradiation and then moves proximally within the adjacent metaphysis after 3 weeks. Corresponding to these findings, histologically a 2-week nadir occurs after irradiation in osteoclasts/chondroclast numbers adjacent to the chondro-osseous junction with a 71.9% decrease compared with controls (p <0.05). At 3 weeks, the numbers of osteoclasts/chondroclasts in this region have increased to 47.4% greater than the control legs (p <0.03) The animals receiving amifostine had BMD that was consistently closer to controls only adjacent to the chondro-osseous junction at 0.5, 2, and 3 weeks and osteoclast/chondroclast numbers that were closer to controls only at 4 weeks.

Body composition, bone mass and microstructural analysis in GH-transgenic mice reveals that skeletal changes are specific to bone compartment and gender

Experimental and clinical studies suggest that high serum levels of growth hormone (GH) increase cortical but not trabecular bone. We studied body composition and bone structure in transgenic mice (MT-bGH) with systemic overexpression of GH. Body composition was examined with dual-energy X-ray absorptiometry (DXA), ashing, and chemical analysis, and the femora with DXA and micro computerized tomography. The absolute fat and bone tissue contents were significantly higher in GH transgenic mice vs controls (P < or = 0.05), but no significant difference was noted when normalizing the values to body weight. Male transgenics displayed no change in apparent (volumetric) femoral bone density, relative cortical area and trabecular bone volume fraction. Female transgenic mice demonstrated an increase in apparent femoral density and in trabecular bone volume fraction (+130%; P < or = 0.01). The mineralized tissue matrix density was decreased in male and female transgenic mice (P < or = 0.05). The results show that chronic GH excess affects trabecular bone in a gender-specific manner and that bone changes depend on the compartment investigated.

Metformin restores responses to insulin but not to growth hormone in Sprague-Dawley rats

Administration of growth hormone (GH) increases muscle mass in F344 x BN rats, but not in Sprague-Dawley (S-D) rats. S-D rats are insulin-resistant and insulin responsiveness is required for the anabolic actions of GH. We hypothesized that correction of insulin resistance with metformin might also restore anabolic effects of GH. Treatment with GH (0.25 or 1.0 mg/kg twice daily for 9 days) had limited anabolic effects, reducing weight gain by 14%, increasing muscle glycogen content by 40% and increasing exercise capacity by 24%, but failing to increase muscle mass or to reduce fat mass. GH also impaired insulin responsiveness and increased visceral fat TNF content of visceral fat by 77%. Metformin enhanced insulin responsiveness in skeletal muscle, but failed to enhance anabolic effects of GH. Rats aged 14 weeks were treated for 21 days with metformin (320 mg/kg/day) and for the last 9 days, with GH (0.25 mg/kg, twice daily). Metformin caused a 2.3-fold increase in insulin-stimulated muscle glucose transport and a 20% reduction in muscle fatty acid oxidation, indicating increased glucose utilization. However, metformin did not augment GH-induced weight reduction. Metformin decreased visceral fat by 22% and subcutaneous fat by 20%, but no decreases were observed in the GH/metformin group. GH increased muscle glycogen by 40%, but the effect was reversed by metformin. VO(2max) was increased 24% by GH and 17% by metformin, but was not elevated in the GH/metformin group. GH increased TNF in visceral fat and the effect was augmented by metformin (144% increase). We conclude that metformin enhances some aspects of insulin responsiveness, but does not enhance anabolic responses to GH. The latter may, in part, be explained by the failure of metformin to prevent GH-induced elevation of TNF in visceral fat.

Systemically administered human growth hormone improves initial implant stability: an experimental study in the rabbit

PURPOSE

This study was an investigation to determine whether human growth hormone (hGH) continuously administered to rabbits may improve implant integration in bone.

MATERIALS AND METHODS

Thirty-two commercially pure titanium (c.p. Ti) implants were inserted in the tibiae of 16 rabbits. Human growth hormone (0.3 U/kg/d) or sodium chloride (NaCl) was administered by subcutaneous pumps. Insulin-like growth factor-1 (IGF-1) levels in blood were measured. Two biomechanical tests were performed: (1) every second week resonance frequency analysis (RFA) was used to investigate implant stability or stiffness at the interface and, after 8 weeks of follow-up, (2) removal torque (a measure of implant integration and stability) was registered. Further evaluation was performed by dual energy x-ray analysis (DEXA), to evaluate bone mineral density, and histomorphometric analysis of tissue-to-implant integration on undecalcified cut and ground sections.

RESULTS

A difference in implant stability was detected with the RFA technique after 2 weeks and 8 weeks in favor of the hGH-treated rabbits. No significant differences were detected with removal torque, DEXA, and histomorphometric measurements. The blood test demonstrated antibody development in the rabbits treated with hGH after 4 weeks.

CONCLUSION

Growth hormone has an initial beneficial effect on implant integration; however, owing to rapid antibody formation, this study did not demonstrate whether this effect remains in the long term.

Decreased trabecular bone biomechanical competence, apparent density, IGF-II and IGFBP-5 content in acromegaly

BACKGROUND

Earlier studies on the effect of excess growth hormone (GH) on trabecular bone have been conflicting. Since insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) in part mediate the effects of GH, the present study aimed to investigate trabecular bone composition of these growth factors in relation to biomechanical properties in acromegaly.

MATERIALS AND METHODS

Trabecular bone biomechanical competence (compression test), apparent density (peripheral quantitative computed tomography, pQCT), and bone matrix contents of calcium (HCl hydrolysis) and IGFs (guanidinium-HCl extraction) were measured in iliac crest biopsies from 13 patients with active acromegaly (two women and 11 men, aged 21-61 years) and 21 age- and sex-matched controls (four women and 17 men, aged 23-64 years).

RESULTS

Trabecular bone pQCT was reduced in acromegalic patients compared with controls (P = 0.005), as was biomechanical competence (P < 0.05 for all measures). These parameters were significantly positively correlated in both acromegalic patients and controls. The calcium content of trabecular bone was significantly increased in patients compared with controls. No significant differences were found in trabecular bone content of IGF-I, IGFBP-3, or osteocalcin. However, IGF-II and IGFBP-5 content was decreased (P < 0.001 and P < 0.05, respectively).

CONCLUSIONS

The present study demonstrates reduced trabecular biomechanical competence and apparent density in acromegaly, supporting previous observations of an unfavourable effect of chronic excess GH on the axial skeleton. Furthermore, we demonstrate decreased trabecular bone content of IGF-II and IGFBP-5 in these patients. However, we found no direct causal relationship between trabecular bone density and bone content of IGF-system components.

Growth hormone therapy during neonatal hypoxia in rats: body composition, bone mineral density, and insulin-like growth factor-1 expression

Hypoxia from birth results in a decrease in body weight gain, body size, and bone mineral density (BMD). The purpose of the present study was to determine whether short-term administration of growth hormone (GH) (rat GH; 100 microg/d) could attenuate some of these effects of neonatal hypoxia. Rat pups (with their lactating dams) were exposed to hypoxia (vs normoxic control) from birth. Hypoxia was continued until 14 d of age, with rat GH (vs vehicle control) administered daily. Hypoxia significantly inhibited body weight gain; GH therapy did not reverse this effect. GH therapy did reverse the inhibitory effect of hypoxia on tail length but not on body length. Hypoxia decreased BMD analyzed by dual X-ray absorptiometry (DXA); this effect was not reversed by GH therapy. Both GH therapy and hypoxia decreased the percentage of body fat analyzed by DXA, the effects of which were additive when combined. There were minimal effects of hypoxia and GH therapy on plasma insulin-like growth factor-1 (IGF-1), IGF-binding protein-3, and hepatic IGF-1 mRNA expression. We conclude that some of the effects of hypoxia on body habitus are reversed by GH therapy, but that short-term GH therapy did not prevent a loss of BMD. GH therapy for more than 14 days may be necessary to appreciate fully its potential in the treatment of the sequelae of neonatal hypoxia.

Validation of peripheral dual-energy X-ray absorptiometry for the measurement of bone mineral in intact and excised long bones of rats

We evaluated the precision and accuracy of peripheral dual-energy X-ray absorptiometry (DXA) for the measurement of bone mineral density (BMD) and bone mineral content (BMC) in intact and excised femurs and tibias from rats. Thirty-one Sprague-Dawley rats (18F/13M; 114-360 g) were used in the study. Precision and accuracy were determined in 23 rats and prediction equations were evaluated in an independent sample of 8 animals. Precision was determined by measuring the right hindquarter three times with repositioning between scans. The femur and tibia were then excised, cleaned, and scanned in triplicate, with repositioning. CVs ranged from 0.66 to 2.24%. Accuracy of BMC was determined by comparison to bone ash values. BMC values for the intact and excised femur significantly overestimated bone ash (p < 0.001) by 33% and 5.5%, respectively. BMC for the intact tibia overestimated ash by 37% (p < 0.001), whereas BMC for the excised tibia underestimated ash by 1% (p < 0.05). However, BMC and bone ash were highly related for both bones, whether BMC was measured in the intact animal or after excision (r2 > 0.99). Cross-validation of prediction equations in an independent sample showed that there were no significant differences between predicted ash (based on BMC from DXA) and measured bone ash. These results suggest the peripheral DXA is a useful tool for measuring intact and excised rat leg bones.

On exposure to anorexia nervosa, the temporal variation in axial and appendicular skeletal development predisposes to site-specific deficits in bone size and density: a cross-sectional study

Skeletal development is heterogeneous. Throughout growth, bone size is more maturationally advanced than the mineral being accrued within its periosteal envelope; before puberty, appendicular growth is more rapid than axial growth; during puberty, appendicular growth slows and axial growth accelerates. We studied women with differing age of onset of anorexia nervosa to determine whether this temporal heterogeneity in growth predisposed to the development of deficits in bone size and volumetric bone mineral density (vBMD), which varied by site and severity depending on the age at which anorexia nervosa occurred. Bone size and vBMD of the third lumbar vertebra and femoral neck were measured using dual-energy X-ray absorptiometry in 210 women aged 21 years (range, 12-40 years) with anorexia nervosa. Results were expressed as age-specific SDs (mean +/- SEM). Bone width depended on the age of onset of anorexia nervosa; when the onset of anorexia nervosa occurred (1) before 15 years of age, deficits in vertebral body and femoral neck width did not differ (-0.77+/-0.27 SD and -0.55+/-0.17 SD, respectively); (2) between 15 and 19 years of age, deficits in vertebral body width (-0.95+/-0.16 SD) were three times the deficits in femoral neck width (-0.28+/-0.14 SD; p < 0.05 comparing the deficits), (3) after 19 years of age, deficits in the vertebral body width (-0.49+/-0.26 SD; p = 0.05) were half that in women with earlier onset of anorexia nervosa. No deficit in bone width was observed at the femoral neck. Deficits in vBMD at the vertebra and femoral neck were independent of the age of onset of anorexia nervosa but increased as the duration of anorexia nervosa increased, being about 0.5 SD lower at the vertebra than femoral neck. We infer that the maturational development of a region at the time of exposure to disease, and disease duration, determine the site, magnitude, and type of trait deficit in anorexia nervosa. Bone fragility due to reduced bone size and reduced vBMD in adulthood is partly established during growth.

Heterogeneity in the growth of the axial and appendicular skeleton in boys: implications for the pathogenesis of bone fragility in men

Men with spine fractures have reduced vertebral body (VB) volume and volumetric bone mineral density (vBMD). Men with hip fractures have reduced femoral neck (FN) volume and vBMD, site-specific deficits that may have their origins in growth. To describe the tempo of growth in regional bone size, bone mineral content (BMC), and vBMD, we measured bone length, periosteal and endocortical diameters, BMC, and vBMD using dual-energy X-ray absorptiometry in 184 boys aged between 7 and 17 years. Before puberty, growth was more rapid in the legs than in the trunk. During puberty, leg growth slowed while trunk length accelerated. Bone size was more advanced than BMC in all regions, being approximately 70% and approximately 35% of their predicted peaks at 7 years of age, respectively. At 16 years of age, bone size had reached its adult peak while BMC was still 10% below its predicted peak. The legs accounted for 48%, whereas the spine accounted for 10%, of the 1878 g BMC accrued between 7 and 17 years. Peripubertal growth contributed (i) 55 % of the increase in leg length but 78% of the mineral accrued and (ii) 69% of the increase in spine length but 87% of the mineral accrued. Increased metacarpal and midfemoral cortical thickness was caused by respective periosteal expansion with minimal change in the endocortical diameter. Total femur and VB vBMD increased by 30-40% while size and BMC increased by 200-300%. Thus, growth builds a bigger but only slightly denser skeleton. We speculate that effect of disease or a risk factor during growth depends on the regions maturational stage at the time of exposure. The earlier growth of a regions size than mass, and the differing growth patterns from region to region, predispose to site-specific deficits in bone size, vBMD, or both. Regions further from their peak may be more severely affected by illness than those nearer completion of growth. Bone fragility in old age is likely to have its foundations partly established during growth.

Mineral density and bone strength are dissociated in long bones of rat osteopetrotic mutations

Bone mineral density (BMD) and mechanical strength generally show strong positive correlations. However, osteopetrosis is a metabolic bone disease with increased skeletal density radiographically and increased risk of fracture. We have evaluated mechanical strength and mineral density in three osteopetrotic mutations in the rat (incisors-absent [ia/ia], osteopetrosis [op/op], and toothless [tl/tl]) to test the hypothesis that reduced bone resorption in one or more of these mutations results in weaker bones in the presence of greater mineral density and skeletal mass. Peripheral quantitative computed tomography (pQCT) was used to analyze BMD and cross-sectional geometry in the tibial diaphysis and metaphysis as well as the femoral diaphysis and femoral neck. The bending breaking force of tibial and femoral midshafts was obtained using the three-point bending test and femoral neck strength was tested by axial loading. Osteopetrotic mutants were significantly smaller than their normal littermates (NLMs) in each stock. The pQCT analysis showed that BMD and bone mineral content (BMC) were higher than or equal to NLMs in all skeletal sites measured in the osteopetrotic mutants. However, the mechanical breaking force was equal to or lower than their NLMs in all sites. The cross-sectional structure of long bone shafts was markedly different in osteopetrotic mutants, having a thin cortex and a medullary area filled with primary trabecular bone. These results indicate that osteopetrotic mutations in the rat increase bone density and decrease bone strength. The tibial diaphysis was significantly weaker in tl/tl and ia/ia mutants and the tibial metaphysis showed the greatest increase in BMD in all mutants. These data are another illustration that an increased BMD does not necessarily lead to stronger bones.

Normal osteoconduction and repair in and around submerged highly bisphosphonate-complexed hydroxyapatite implants in rat tibiae

BACKGROUND

Ceramic hydroxyapatite implants have been used in dentistry for their unique compatibility with alveolar bone. Recently it was reported that bisphosphonates may be beneficial in preventing alveolar bone destruction associated with natural and experimental periodontal disease. Furthermore, bisphosphonate does prevent resorption of alveolar bone following mucoperiosteal flap surgery. We undertook a preliminary study evaluating the effects of highly bisphosphonate-complexed hydroxyapatite implants on osteoconduction and repair in rat tibiae.

METHODS

Porous hydroxyapatite implants were pre-incubated in 10(-2)M bisphosphonate solutions at pH 3.49 and pH 7.32. The implants had a diameter of 2.1 mm and a height of 2 mm and adsorbed 115 microg bisphosphonate in vitro. Bisphosphonate/hydroxyapatite implants and plain hydroxyapatite implants were inserted in opposite tibial metaphyses of 35 rats. The measurement errors for the mineral density (MD) of the implants and the proximal trabecular mineral bone density (TD) were estimated by peripheral computed tomography and the bone mineral density (BMD) measurement error by dual x-ray absorptiometry.

RESULTS

The measurement errors for the MD of the implants and the TD by peripheral computed tomography were 0.81% and 1.96%, respectively ex vivo. The BMD measurement error estimated by dual x-ray absorptiometry was 0.51% ex vivo. TD and BMD for bisphosphonate/hydroxyapatite implants were insignificantly higher compared to plain hydroxyapatite implants. Bisphosphonate/hydroxyapatite pre-incubated at pH 7.32 were found to be nondegradable implants, while bisphosphonate/hydroxyapatite (pH 3.49) implants were slowly degradable and lost a significant 5% of their density. Histologically, all bisphosphonate/hydroxyapatite implants appeared to be fully integrated and effective as bone replacement material in rat tibial bone. They exhibited vascularization and osteoconduction of tibial bone growth along and inside their porous structure.

CONCLUSIONS

Our study suggests that normal osteoconduction and repair occurred in and around the highly bisphosphonate-complexed hydroxyapatite implants in rat tibiae.

Femoral neck is a sensitive indicator of bone loss in immobilized hind limb of mouse

The present study was carried out to evaluate a unilateral hind limb immobilization model in the mouse. The right legs of male mice (age 10-12 weeks) were immobilized for 3 weeks against the abdomen by an elastic bandage. Body weight decreased significantly during the immobilization. Peripheral quantitative computed tomography (pQCT) analysis showed that the cross-sectional cortical area (CSA), the bone mineral content (BMC), and the bone mineral density (BMD) of the tibial diaphysis were lower in both legs of the immobilized animals than in age-matched controls, but the difference was mainly due to weight reduction. At the tibial metaphysis, CSA, BMC, and BMD were reduced in both legs of the immobilized animals, even after weight adjustment. At the femoral neck, CSA, BMC, and BMD were significantly lower in both legs of the immobilized animals, and the difference between the hind legs of the immobilized animals was also highly significant. The findings of the pQCT study were in good agreement with the changes in mechanical strength. The tibia was a more sensitive indicator of diaphyseal bone weakening than the femur when measuring the bending breaking force of the diaphysis. The femoral neck showed significantly decreased strength, and the difference between the immobilized leg and the contralateral leg was most clearly seen in lateral loading. We conclude that 3 weeks of hind limb immobilization weakened the tibia and femur significantly compared with their contralateral counterparts. The reduction was more significantly seen in the mechanical bending strength than in the pQCT evaluation, and the femoral neck was the most sensitive indicator of bone weakening.

The differing tempo of growth in bone size, mass, and density in girls is region-specific

The differing tempo and direction of growth of the periosteal and endocortical surfaces, and the differing tempo of growth of the axial and appendicular skeleton, may predispose to regional deficits in bone size, bone mineral content (BMC), and volumetric bone mineral density (vBMD). These traits were measured during 2 years by dual x-ray absorptiometry in 109 girls. By 7 years of age, bone size was approximately 80% of its maturational peak, and BMC was approximately 40% of its peak. Before puberty, the legs grew more rapidly than the trunk. During puberty, the growth spurt was truncal. Between 7 and 17 years, femoral and lumbar spine BMC increased by 50-150% because bone size increased. vBMD increased by 10-30%. Thus, growth builds a bigger, but only moderately denser, skeleton. Regions growing rapidly, or distant from their peak, may be more severely affected by illness than those growing slowly or nearer completion of growth. Depending on the age of exposure to disease, deficits may occur in limb dimensions (prepuberty), spine dimensions (early puberty), or vBMD by interference with mineral accrual (late puberty). As vBMD is independent of age before puberty, the position of an individual's vBMD in the population distribution is established early in life. Bone fragility in old age may have its foundations in growth.

Hexarelin, a growth hormone - releasing peptide, counteracts bone loss in gonadectomized male rats

The age-related decline in growth hormone (GH) secretion has been implicated in the pathogenesis of involutional bone loss. Whether restoration of GH secretion might be helpful in maintaining and/or improving bone mass during aging is still unsettled. The aim of the present study was to examine the effects of 30-day treatment with hexarelin (HEXA, 50 microg/kg subcutaneously b.i.d.), a highly effective GH-releasing compound, on bone metabolism and bone mineral density (BMD) in intact and osteopenic gonadectomized (GDX) mature male rats. Serum total alkaline phosphatase (ALP, bone formation marker) and bone resorption markers (lysylpyridinoline, LP and hydroxylysylpyridinoline, HP) were measured before and 7, 14 and 30 days after treatment. BMD was measured by dual-energy X-ray absorptiometry at lumbar vertebrae, femoral metaphysis and diaphysis before and at the end of the experiment. In intact rats, HEXA significantly (P<0.05) decreased LP (-36.3%) and HP (-22.8%) excretion at day 7, whereas it did not change serum ALP activity and BMDs. In GDX rats, HEXA completely prevented the significant (P<0. 01) increase in urinary excretion of both LP (+143.8%) and HP (+119. 4%), the early decrease in ALP activity (-26.5%) and the significant (P<0.05) decrease in BMDs in the femoral metaphysis (-7.9%) and lumbar vertebrae (-6.8%) caused by androgen deficiency. The bone-protective effects of HEXA could be attributed, at least in part, to its GH-releasing activity since chronic-treated rats maintained the GH response to an acute challenge with HEXA. The evidence that HEXA, unlike GH, inhibits bone resorption indicates that other mechanisms contribute to the bone sparing effect of HEXA.

Targeted expression of calcitonin gene-related peptide to osteoblasts increases bone density in mice

The neuropeptide calcitonin gene-related peptide (CGRP) is concentrated in fine sensory nerve endings innervating all tissues, including bone. CGRP inhibits osteoclasts, stimulates insulin-like growth factor I and inhibits tumor necrosis factor alpha production by osteoblasts in vitro. To investigate the role of CGRP in bone in vivo, mice were engineered to express CGRP in osteoblasts by placing the human CGRP gene under the control of the rat osteocalcin promoter (Ost-CGRP tg+ mice). Calvaria cultures from transgene positive (tg+), but not tg- mice, produced bioactive CGRP. Trabecular bone density and bone volume, determined by peripheral quantitative computed tomography and bone histomorphometry, respectively, were higher in tg+ than tg- littermates. This increase in bone volume was associated with an increased bone formation rate. Trabecular bone density decreased in tg+ mice as a result of ovariectomy, but remained higher than in sham tg- mice. Targeting CGRP to osteoblasts appears to favor the establishment of a higher trabecular bone mass in mice.

The structural basis of bone fragility in men

Understanding of the pathogenesis of bone fragility in men requires knowledge of its structural basis. There is no evidence that gender differences in fracture rates are explained by gender differences in bone mineral content (BMC) or areal bone mineral density (BMD). This is an untested assumption. The BMD measurement integrates the modeling and remodeling that occurs on the periosteal and endosteal surfaces of bone during growth and aging. The size, shape, and architecture of the bone so formed determine its breaking strength. None of these three-dimensional structural components is "seen" by the dual photons of the densitometer. Men and women attain a similar peak vertebral height during growth. Vertebral width is greater in men, conferring higher BMC and areal BMD, but trabecular number and thickness (trabecular volumetric BMD) is no greater in men than women. Blacks have shorter vertebra than whites, and vertebral width is similar. Trabecular thickness is greater in blacks than whites. Thus, at peak, gender differences in vertebral strength are likely to be size, not BMD, dependent. Racial differences in vertebral strength are likely to be BMD, not size, dependent. Greater periosteal expansion during growth in males than females, and blacks than whites, establishes the gender and racial differences in peak bone size. Men have wider long bones than women. Blacks have wider long bones than whites. The proximity of the endocortical surface to the periosteal surface determines peak cortical width, which is similar in men, women, blacks, and whites. It is the greater distance of the cortical mineral mass from the neutral axis of a long bone in males than in females, in blacks than in whites, and in men with, than men without, fractures, that partly accounts for the greater bone strength in the first mentioned in each group. Thus, at peak, racial and gender differences in long bone strength are likely to be size, not BMD dependent. Trabecular bone loss is similar in men and women. Loss of connectivity is greater in women. Endocortical resorption is greater in women than men, but men lose less cortical width because subperiosteal apposition during aging is greater in men than in women offsetting endocortical resorption. Men with spine fractures have smaller vertebrae because vertebral width is less. Men with hip fractures have smaller femoral neck width. In both types of fractures, there is less bone in the smaller bone-reduced volumetric BMD. The relative contributions of reduced accrual during growth, excessive bone loss during aging, or both to the deficit in volumetric BMD are undefined. No antifracture efficacy trials have been done in men. Reasonable approaches to treatment include the use of testosterone in hypogonadal men, and vitamin D if vitamin D deficiency is present. Calcium supplements may slow endocortical bone loss. Bisphosphonates may increase BMD.

The effects of gonadectomy on bone size, mass, and volumetric density in growing rats are gender-, site-, and growth hormone-specific

Peak volumetric bone mineral density (BMD) is determined by the growth in bone size relative to the mineral accrued within its periosteal envelope. Thus, reduced peak volumetric BMD may be the result of reduced mineral accrual relative to growth in bone size. Because sex steroids and growth hormone (GH) influence bone size and mass we asked: What are the effects of gonadectomy (Gx) on bone size, bone mineral content (BMC), areal and volumetric BMD in growing male and female rats? Does GH deficiency (GH-) reduce the amount of bone in the (smaller) bone, i.e., reduce volumetric BMD? Does GH- alter the effect of Gx on bone size and mineral accrual? Gx or sham surgery was performed at 6 weeks in GH- and GH replete (GH+) Fisher 344 male and female rats. Changes in bone size, volume, BMC, areal and volumetric BMD, measured using dual X-ray absorptiometry (DPX-L), were expressed as percentage of controls at 8 months (mean +/- SEM). All results shown were significant (p < 0.05 level) unless otherwise stated. In GH+ and GH- males, respectively, Gx was associated with: lower femur volume (24%, 25%), BMC (43%, 45%), areal BMD (21%, 14%), and volumetric BMD (30%, 28%); lower spine (L1-L3) volume (26%, 28%), BMC (26%, 30%), and areal BMD (28%, 12%), but not volumetric BMD. Following Gx, GH+ females had increased femur volume (11%), no effect on BMC, decreased areal BMD (6%) and decreased volumetric BMD (17%); GH- females had no change in femur volume, but decreased femur BMC (24%), areal BMD (10%), and volumetric BMD (25%). In GH+ and GH- females, respectively, Gx was associated with a decrease in spine (L1-L3) BMC (12%, 15%), areal BMD (16%, 15%), and volumetric BMD (10%, 16%) with no change in volume. Deficits in non-Gx GH- relative to non-Gx GH+ (males, females, respectively) were: femur BMC (49%, 37%), areal BMD (23%, 8%), volume (19%, 19%) and volumetric BMD (37%, 22%); spine (L1-L3) BMC (46%, 42%), areal BMD (37%, 43%), volume (10%, 15%), and volumetric BMD (40%, 33%). Testosterone and GH are growth promoting in growing male rats, producing independent effects on bone size and mass; deficiency produced smaller appendicular bones with reduced volumetric BMD because deficits in mass were greater than deficits in size. At the spine, the reduction in size and accrual were proportional, resulting in a smaller bone with normal volumetric BMD. In growing female rats, estrogen was growth limiting at appendicular sites; deficiency resulted in a GH-dependent increase in appendicular size, relatively reduced accrual, and so, reduced volumetric BMD in a bigger bone. At the spine, accrual was reduced while growth in size was normal, thus volumetric BMD was reduced in the normal sized bone. Understanding the pathogenesis of low volumetric BMD requires the study of the differing relative growth in size and mass of the axial and appendicular skeleton in the male and female and the regulators of the growth of these traits.

Trabecular bone mineral and calculated structure of human bone specimens scanned by peripheral quantitative computed tomography: relation to biomechanical properties

The relationship of cortical bone mineral density (BMD), and geometry to bone strength has been well documented. In this study, we used peripheral quantitative computerized tomography (pQCT) to acquire trabecular BMD and high-resolution images of trabeculae from specimens to determine their relationship with biomechanical properties. Fifty-eight human cubic trabecular bone specimens, including 26 from the vertebral bodies, were scanned in water and air. Trabecular structure was quantitated using software developed with Advanced Visual Systems interfaced on a Sun/Sparc Workstation. BMD was also obtained using a whole-body computerized tomography scanner (QCT). Nondestructive testing of the specimens was performed to assess their elastic modulus. QCT and pQCT measurements of BMD of specimens in water were strongly correlated (r2 = 0.95, p < 0.0001), with a slope (0.96) statistically not significantly different from 1. Strong correlations were found between pQCT measurements of specimens in water and in air, for BMD (r2 = 0.96, p < 0.0001), and for apparent trabecular structural parameters (r2 = 0.89-0.93, p < 0.0001). Correlations were moderate between BMD and apparent trabecular structural parameters (r2 = 0.37-0.64, p < 0.0001). Precision as coefficient of variation (CV) and standardized coefficient of variation (SCV) for these measurements was < 5%. For the vertebral specimens, the correlation was higher between elastic modulus and BMD (r2 = 0.76,p < 0.0001) than between elastic modulus and apparent trabecular structural parameters (r2 = 0.58-0.72, p < 0.0001), while the addition of apparent trabecular nodes and branches to BMD in a multivariate regression model significantly increased the correlation with the elastic modulus (r2 = 0.86, p < 0.01). Thus, pQCT can comparably and reproducibly measure trabecular bone mineral in water or air, and trabecular structure can be quantitated from pQCT images. The combination of volumetric BMD with trabecular structural parameters rather than either alone improves the prediction of biomechanical properties. Such a noninvasive approach may be useful for the preclinical study of osteoporosis.

Clinical evaluation of a high-resolution new peripheral quantitative computerized tomography (pQCT) scanner for the bone densitometry at the lower limbs

Precision, long-term stability, linearity and accuracy of the x-ray peripheral quantitative computerized tomographic (pQCT) bone scanner XCT 3000 (Norland-Stratec Medical Sys.) were evaluated using the European Forearm Phantom (EFP). In vivo measurements were assessed using a standardized procedure at the distal femur and the distal tibia. In the patient-scan mode, the spatial resolution of the system was 1.04 +/- 0.05 lp/mm as measured at the 10% level of the modulation transfer function (MTF). The contrast-detail diagram (CDD) yielded a minimal difference in attenuation coefficient (AC) of 0.07 cm(-1) at an object size of 0.5 mm. The effective dose for humans was calculated to be less than 1.5 microSv per scan. Short-term precision in vivo was expressed as root mean square standard deviation of paired measurements of 20 healthy volunteers (RMSSD = 0.5%). At the distal femur total volumetric density (ToD) and total cross-sectional area (ToA) were found to be less sensitive to positioning errors than at the distal tibia. Structural parameters like the polar cross-sectional moment of inertia (CSMIp) or the polar cross-sectional moment of resistance (CSMRp) showed a good short-term precision at the distal femur (RMSSD = 1.2 and 1.4%). The relation between the two skeletal sites with respect to CSMIp or CSMRp showed a high coefficient of determination (r2 = 0.77 and 0.74).

Growth hormone therapy and fracture risk in the growth hormone-deficient adult

Adults with childhood-onset growth hormone deficiency (GHD) and younger adults with adult-onset GHD have a reduced bone mineral content (BMC). Recent trials with prolonged GH replacement therapy have demonstrated increased BMC in such patients. GH treatment in animals increases the amount of bone and the total strength while the density (BMC per unit volume) and the quality of the bone is not increased. A sensitive non-invasive parameter for the detection of effects of GH on bone in clinical studies is therefore to use the BMC from dual-energy X-ray absorption (DEXA) analysis. Bone density is strongly related to fracture risk in women. A number of other risk factors for fractures can be identified in adult GHD patients which, collectively, might explain the increased fracture frequency observed in these patients. The increase in BMC in response to long-term GH replacement therapy is promising. Whether more prolonged treatment will result in a normalization of the bone mass and reduced fracture frequency remains to be established.

Bone mineral, histomorphometry, and body composition in adults with growth hormone receptor deficiency

Growth hormone (GH) and insulin-like growth factor I (IGF-I) deficiencies have been associated with osteopenia in both children and adults. To examine the effects of growth hormone resistance on bone mineral and body composition, we studied 11 adults (mean age 30 years) with growth hormone receptor deficiency (GHRD, Laron syndrome) and 11 age- and gender-matched controls from Southern Ecuador. Bone mineral and body composition were determined by dual-energy X-ray absorptiometry. Bone physiology was assessed with biochemical markers of bone turnover and dynamic bone histomorphometry. Bone size and body composition differed markedly between subjects with GHRD and controls. Affected adults were 40 cm shorter than controls, had significantly less lean body mass, and had increased percent body fat. Bone mineral content and density (BMD) at the spine, femoral neck, and whole body were significantly lower in adults with GHRD than in controls. Mean BMD Z scores were -1.5 to -1.6 at all sites in affected women and -2.2 to -2.3 in men with GHRD. Estimated volumetric bone density (BMAD) at the spine and femoral neck, however, was not reduced in GHRD. Spine BMAD was 0.210 +/- 0.025 versus 0.177 +/- 0.021 for affected women versus controls (p < 0.05) and 0.173 +/- 0.018 versus 0.191 +/- 0.025 for men with GHRD versus normals (p = 0.31). Urinary pyridinoline concentrations were significantly greater in adults with GHRD than in controls, while type I collagen C-telopeptide breakdown products and markers of bone formation did not differ. Differences in histomorphometry were limited to a reduction in trabecular connectivity; bone volume and formation rate were similar to controls. These data confirm the importance of the GH/IGF axis in regulating bone size and body composition. The contribution of these peptides to the acquisition and maintenance of bone mineral is less certain since volumetric bone density was preserved despite low levels of IGF-I and IGFBP-3 associated with GH resistance.

Fluoride potentiates the osteogenic effects of IGF-I in aged ovariectomized rats

The molecular mechanisms whereby fluoride stimulates osteogenic cell proliferation are not clearly established. However, fluoride has been shown to enhance the protein tyrosine phosphorylation of various constituents of intracellular signaling cascades in osteoblastic cells following stimulation of growth factor receptors such as the insulin-like growth factor-I (IGF-I) receptor. Such in vitro findings provided the rationale for testing whether the administration of fluoride could enhance IGF-I effects on bone mass in vivo. Adult ovariectomized osteopenic rats were treated with sodium fluoride at a dose of 6 mg/kg per day in drinking water for 8 weeks in association with IGF-I either at a dose of 2 mg/kg per day, which is capable of increasing bone mass, or at a lower dose without detectable skeletal effects. Bone mineral density (BMD) and content (BMC) were evaluated by dual-energy X-ray absorptiometry at the levels of the lumbar spine and proximal, midshaft, and total tibia before and after 8 weeks of treatment. During this period, fluoride alone did not significantly influence BMD/BMC at any skeletal site. However, it potentiated the effect of the higher dose of IGF-I on bone mass at the level of the proximal tibia. When administered in combination with the lower dose of IGF-I, which per se did not modify bone mass, it appeared to sensitize tibial bone to the effects of IGF-I. These changes were associated with a concomitant increase in osteocalcin, taken as a reflection of bone formation. These results indicate that fluoride could potentiate the osteogenic effects of IGF-I on bone in adult ovariectomized rats.

Aromatase inhibition impairs skeletal modeling and decreases bone mineral density in growing male rats

Aromatization of androgens into estrogens may explain some of the skeletal action of androgens. We examined the effect of the aromatase inhibitor Vorozole (VOR) on skeletal growth and mineral accumulation in growing 6-week-old male Wistar rats. Rats were either Sham-operated (Sham) or Orchidectomized (Orch) and treated with or without the aromatase inhibitor VOR. One Sham-operated group was killed at Baseline (Base); the four other groups (Sham, Sham + VOR, Orch, Orch + VOR) were killed 18 weeks after surgery. As expected, all groups gained body weight, but body weight gain was significantly (-25%) lower in Orch, Orch + VOR, and Sham + VOR. Both bone formation, as assessed by serum osteocalcin, and bone resorption, as assessed by urinary (deoxy)pyridinoline, decreased significantly in all groups compared with Base. Orchidectomy resulted in a relative increase of biochemical markers of bone formation and resorption compared with Sham. Treatment with VOR, however, resulted only in a very moderate increase of (deoxy)pyridinoline compared with Sham. As expected, femoral length increased compared with Base, but orchidectomy reduced the relative growth of the femur whereas VOR did not influence femoral length. Ex vivo, densitometric and geometric properties of the femora were evaluated by peripheral computerized quantitative tomography (pQCT) and dual-energy x-ray absorptiometry (DXA). The lumbar vertebrae were measured by DXA. At the end of the experimental period, volumetric trabecular bone mineral density (vTBMD) measured at the distal end of the femur was significantly lower not only in both Orch groups but also in Sham + VOR. The decrease of cancellous bone density in Sham + VOR was lower than in the orchidectomized animals. A relative decrease of femoral inner and outer diameters compared with Sham and Base was observed in both Orch groups and in Sham + VOR, suggesting that both orchidectomy and VOR-treatment inhibited periosteal bone formation and endosteal bone resorption. Only orchidectomy, however, resulted in a decrease of cortical thickness. Bone area, mineral content, and density of both femora and lumbar vertebrae, measured by DXA, were decreased to a similar extent by VOR and Orch (bone mineral content of the femur was 467 +/- 18 mg in Orch and 461 +/- 10 mg in Sham +/- VOR vs. 521 +/- 11 mg in Sham; P < 0.001). In conclusion, treatment with the aromatase inhibitor VOR impairs body weight gain and skeletal modeling and decreases bone mineral density. Aromatase inhibition had similar final effects on bone mass and size as castration, but with less marked effects on bone turnover.

Changing femoral geometry in growing girls: a cross-sectional DEXA study

In elderly women, a long hip axis length has been shown to increase the risk of hip fracture. However, to date, few measurements of hip geometry have been reported in children and adolescents. The present cross-sectional dual-energy X-ray absorptiometry (DEXA) study of 200 girls aged 3-16 years was undertaken to determine at what age adult hip geometry is achieved and to examine possible influences of anthropometry and body composition on the development of femur axis length (FAL) and femur width (FW) during growth. Adult values for FAL and FW were achieved by age 15 years. Age, height, lean tissue mass, total body bone mineral content (BMC), weight, FW, neck of femur bone mineral density (BMD), and fat were each strongly associated with FAL (p < 0.001), the highest correlations being with age (r = 0.917) and height (r = 0.906). However, after adjusting for age and height, only lean tissue mass, weight, and fat mass remained significantly associated with FAL, suggesting that bone mineral accrual does not influence variance in FAL. Our results also suggested that fat mass and weight per se tended to have greater influence on FW than on FAL in age- and height-adjusted data. Twin studies indicate that 20% of adult hip axis length is associated with environmental factors. We therefore conclude that any environmental effects of physical activity or nutrition on hip geometry must occur before early teen-age years.

Genetic variability in adult bone density among inbred strains of mice

More than 70% of the variability in human bone density has been attributed to genetic factors as a result of studies with twins, osteoporotic families, and individuals with rare heritable bone disorders. We have applied the Stratec XCT 960M pQCT, specifically modified for small skeletal specimens, to analyses of bones from 11 inbred strains (AKR/J, BALB/cByJ, C3H/HeJ, C57BL/6J, C57L/J, DBA/2J, NZB/B1NJ, SM/J, SJL/BmJ, SWR/BmJ, and 129/J) of female mice to determine the extent of heritable differences in peak bone density, pQCT scans were taken of femurs from (a) 12-month-old inbred strain females and (b) a subset of four strains (C3H/HeJ, DBA/2J, BALB/cByJ, C57BL/6J) at 2, 4, and 8 months. In addition, pQCT scans were also obtained from L5-L6 vertebrae and proximal phalanges from the same subset of four inbred strains at 12 months of age. Comparison of bone parameters among inbred strains revealed significant differences at each of the three sites investigated. Femoral and phalangeal bones differed among strains with respect to total and cortical density, mineral, and volume. Only cortical bone parameters were significantly different among strains at the vertebral site. With respect to strain differences, the highest value for any given bone parameter was found in the C3H/HeJ strain, whereas C57BL/6J values were absolutely, or statistically, the lowest. Similarly, with respect to bone sites, cortical bone density was significantly correlated among strains. On the other hand, we found that none of the femur, vertebral, or phalangeal parameters correlated with body weight, even though body weight varied by 86% among those inbred strains. The developmental studies of femurs conducted at 2, 4, and 8 months of age with C3H/HeJ, DBA/2J, BALB/cByJ, and C57BL/6J females showed differences in total density among strains at 2 months and thereafter. Adult peak bone density was typically achieved by 4 months, whereas femurs continued to lengthen for 4 to 8 months thereafter. We conclude that (1) major genetic effects on femoral, vertebral, and phalangeal bone density are detectable among inbred strains of mice; (2) cortical bone density shares common genetic regulation at the three measured sites; and (3) within the femur, genes that regulate length and density are different.