Treatment of ovariectomized rats with the complex of rhIGF-I/IGFBP-3 increases cortical and cancellous bone mass and improves structure in the femoral neck

MicroCT analyses of mouse femoral neck architecture

Hip fractures at the femoral neck are a major cause of morbidity and mortality, but aside from biomechanical strength testing, little is known about femoral neck architecture in mice. Procedures were optimized to analyze high-resolution (6 μm voxel size) microCT scans of the mouse femoral neck to provide bone mass and architectural information. Similar to histomorphometric observations in rats, the boundary between cortical and trabecular bone is difficult to identify in the mouse femoral mid-neck and these compartments were not analyzed separately. Analyses included total area, mineralized bone area, and bone volume fraction (BV/TV). Femoral neck architecture varies in C57BL/6J, 129/SvEv and BALB/c mouse strains. Bone cross sectional area and BV/TV were low in Lrp5 but elevated in Sost gene knockout mice. Sfrp4 gene knockout resulted in high total area, normal bone area, low BV/TV and, as indicated by BS/BV values, greater trabecularization. Femoral neck BV/TV declined with age and ovariectomy, but increased with teriparatide treatment. These findings demonstrate that the architecture of the mouse femoral neck mimics phenotypes and treatment effects observed at other skeletal sites and is a relevant bone site for translational studies examining osteoporosis therapies.

Function of matrix IGF-1 in coupling bone resorption and formation

Balancing bone resorption and formation is the quintessential component for the prevention of osteoporosis. Signals that determine the recruitment, replication, differentiation, function, and apoptosis of osteoblasts and osteoclasts direct bone remodeling and determine whether bone tissue is gained, lost, or balanced. Therefore, understanding the signaling pathways involved in the coupling process will help develop further targets for osteoporosis therapy, by blocking bone resorption or enhancing bone formation in a space- and time-dependent manner. Insulin-like growth factor type 1 (IGF-1) has long been known to play a role in bone strength. It is one of the most abundant substances in the bone matrix, circulates systemically and is secreted locally, and has a direct relationship with bone mineral density. Recent data has helped further our understanding of the direct role of IGF-1 signaling in coupling bone remodeling which will be discussed in this review. The bone marrow microenvironment plays a critical role in the fate of mesenchymal stem cells and hematopoietic stem cells and thus how IGF-1 interacts with other factors in the microenvironment are equally important. While previous clinical trials with IGF-1 administration have been unsuccessful at enhancing bone formation, advances in basic science studies have provided insight into further mechanisms that should be considered for future trials. Additional basic science studies dissecting the regulation and the function of matrix IGF-1 in modeling and remodeling will continue to provide further insight for future directions for anabolic therapies for osteoporosis.

Impaired expression of insulin-like growth factor-1 system in skeletal muscle of amyotrophic lateral sclerosis patients

Introduction

Adult muscle fibers are a source of growth factors, including insulin-like growth factor-1 (IGF-1). These factors influence neuronal survival, axonal growth, and maintenance of synaptic connections.

Methods

We investigated the components of the IGF system in skeletal muscle samples obtained from 17 sporadic amyotrophic lateral sclerosis patients (sALS) and 29 control subjects (17 with normal muscle and 12 with denervated muscle unrelated to ALS).

Results

The muscle expression of IGF-1 and IGF-binding proteins 3, 4, and 5 (IGF-BP3, -4, and -5, respectively), assessed by immunohistochemistry, was differently decreased in sALS compared with both control groups; conversely, IGF-1 receptor β subunit (IGF-1Rβ) was significantly increased. Western blot analysis confirmed the severe reduction of IGF-1, IGF-BP3, and -BP5 with the increment of IGF-1Rβ in sALS.

Conclusion

In this study we describe the abnormal expression of the IGF-1 system in skeletal muscle of sALS patients that could participate in motor neuron degeneration and should be taken into account when developing treatments with IGF-1. Muscle Nerve, 2012

The -202 A allele of insulin-like growth factor binding protein-3 (IGFBP3) promoter polymorphism is associated with higher IGFBP-3 serum levels and better growth response to growth hormone treatment in patients with severe growth hormone deficiency

CONTEXT

Genetic factors that influence the response to recombinant human GH (rhGH) therapy remain mostly unknown. To date, only the GH receptor gene has been investigated.

OBJECTIVE

The aim of the study was to assess the influence of a polymorphism in the IGF-binding protein-3 (IGFBP-3) promoter region (-202 A/C) on circulating IGFBP-3 levels and growth response to rhGH therapy in children with GH deficiency (GHD).

DESIGN AND PATIENTS

-202 A/C IGFBP3 genotyping (rs2854744) was correlated with data of 71 children with severe GHD who remained prepubertal during the first year of rhGH treatment.

MAIN OUTCOME MEASURES

We measured IGFBP-3 levels and first year growth velocity (GV) during rhGH treatment.

RESULTS

Clinical and laboratory data at the start of treatment were indistinguishable among patients with different -202 A/C IGFBP3 genotypes. Despite similar rhGH doses, patients homozygous for the A allele presented higher IGFBP-3 sd score levels and higher mean GV in the first year of rhGH treatment than patients with AC or CC genotypes (first year GV, AA = 13.0 +/- 2.1 cm/yr, AC = 11.4 +/- 2.5 cm/yr, and CC = 10.8 +/- 1.9 cm/yr; P = 0.016). Multiple linear regression analyses demonstrated that the influence of -202 A/C IGFBP3 genotype on IGFBP-3 levels and GV during the first year of rhGH treatment was independent of other variables.

CONCLUSION

The -202 A allele of IGFBP3 promoter region is associated with increased IGFBP-3 levels and GV during rhGH treatment in prepubertal GHD children.

Mecasermin rinfabate: rhIGF-I/rhIGFBP-3 complex: iPLEX

BACKGROUND

Mecasermin rinfabate (iPLEX), comprising rhIGF-I complexed to rhIGFBP-3, was developed in an attempt to prolong the half-life of IGF-I and potentially reduce side effects. It is administered as a once-daily subcutaneous injection. Treatment with rhIGF-I has been explored in a number of growth and endocrine disorders.

OBJECTIVE

To review the published literature regarding the pharmacokinetics, safety profile and clinical efficacy of Mecasermin rinfabate.

METHODS

A comprehensive search via the NCBI PubMed portal was performed using the search terms rhIGF-I/rhIGFBP-3 complex, iPLEX and Somatokine.

RESULTS

The effects of Mecasermin rinfabate have been explored in a number of clinical situations including diabetes, severe insulin resistance, osteopaenia, burns and growth hormone insensitivity syndrome, with outcomes similar to those of rhIGF-I alone.

CONCLUSIONS

The biological effects of Mecasermin rinfabate are largely similar to those previously reported with rhIGF-I. There are little published data pertaining to pharmacokinetic properties in human subjects, and the side effect profile appears similar to that of rhIGF-I alone.

Contrasting bone effects of temporary versus permanent IGFBP administration in rodents

Transgenic animal technology has tremendously improved our current comprehension of IGFBP biology. The high potential of IGFBP transgenic mouse models is due to the fact that they mimic elevated serum IGFBP levels, which are diagnosed under the conditions of impaired growth or critical illness. In general, long term elevated levels of IGFBPs in transgenic mouse models almost exclusively resulted in inhibitory phenotypes e.g. of body or organ growth, indicating specific effects in different cell types. This holds especially for the distinct cellular populations present in the bone environment. After establishing transgenic mouse lines modelling permanent increases of IGFBPs, a second question now poses challenge to current functional genome analysis: what is the function of temporary exposure of a certain cell type to isolated IGFBPs? This question is particularly important due to the fact that elevated IGFBP expression is often found in a conditional fashion and in line with the contradictory findings after long or short term IGFBP exposure in rodent models. In order to understand the potential roles of the conditional increases of IGFBP expression, e.g. during illness, and to further study the adaptive or even therapeutic potential of IGFBPs for certain applications like osteoporosis, it is imperative to take a closer look also to the acute effects of the IGFBPs.

Effects of insulin-like growth factor binding proteins in bone -- a matter of cell and site

The actions of the insulin-like growth factor (IGF)-system are controlled by six IGF-binding proteins (IGFBPs). The IGFBPs are thought to affect local effects of IGF-I and IGF-II due to higher affinity if compared to IGF-I receptors and due to cell-type specific IGFBP expression patterns. It was found in IGFBP knockout models that the IGFBP family is functionally redundant. Thus, functional analysis of potential effects of IGFBPs is dependent on descriptive studies and models of IGFBP overexposure in vitro and in vivo. In the literature, the role of the IGFBPs for bone growth is highly controversial and, to date, no systematic look has been taken at IGFBPs resolving functional aspects of IGFBPs at levels of cell types and specific locations within bones. Since IGFBPs are thought to represent local modulators of the IGF actions and also exert IGF-independent effects, this approach is particularly reasonable on a physiological level. By sorting the huge number of in part controversial results on IGFBP effects in bone present in the literature for distinct cell types and bone sites it is possible to generate a focused, more specific and a less controversial picture of IGFBP functions in bone.

Somatotropic and gonadotropic axes linkages in infancy, childhood, and the puberty-adult transition

Integrative neuroendocrine control of the gonadotropic and somatotropic axes in childhood, puberty, and young adulthood proceeds via multiple convergent and divergent pathways in the human and experimental animal. Emerging ensemble concepts are required to embody independent, parallel, and interacting mechanisms that subserve physiological adaptations and pathological disruption of reproduction and growth. Significant advances in systems biology will be needed to address these challenges.

Insulin-like growth factor-I and parathyroid hormone: potential new therapeutic agents for the treatment of osteoporosis

Millions of men and women worldwide are afflicted by osteoporosis. As this number is projected to increase over the next half century, attempts to forestall the disease process are being tested. Conventional therapies centre on maintaining bone mineral density (BMD) by blocking bone resorption. However, there is a growing need for drugs that can stimulate new bone formation (anabolic agents), thereby reducing future fracture risk. Both parathyroid hormone (PTH) and insulin like growth factor-I (IGF-I) have been the subject of numerous animal and human studies to determine whether these peptides have promise for the treatment of low bone mass. Although the mechanisms of action for these agents are not well delineated, each protein can activate the osteoblast and thereby enhance bone mass. The effects of these drugs on the osteoclast are less well defined. At the current time, there is considerably more interest in PTH than IGF-I, for several reasons. Firstly, animal studies with PTH are more impressive in terms of histomorphometry and biomechanics than IGF-I; secondly, PTH is specific for the skeleton whereas IGF-I is ubiquitous; and thirdly, human studies with PTH have been relatively devoid of significant side-effects. Large scale Phase III trials are now underway in the US and Europe. It is anticipated that at least one of these peptides may prove to have a role in the prevention and treatment of osteoporosis.

Skeletal growth and long-term bone turnover after enterocystoplasty in a chronic rat model

OBJECTIVE

To investigate skeletal growth and bone metabolism in a chronic animal model of urinary diversion.

MATERIALS AND METHODS

Young male Wistar rats (120) were allocated randomly to four groups undergoing: ileocystoplasty, ileocystoplasty and resection of the ileocaecal segment, colocystoplasty, and controls. All animals received antibiotics for 1 week after surgery; half of each group remained on oral antibiotics. Bone-related biochemistry was measured in serum and urine. Dual-energy X-ray absorptiometry and peripheral quantitative computed tomography (pQCT) were used to determine bone mass ex vivo.

RESULTS

Most (90%) of the rats survived the study period (8 months); six rats died from bowel obstruction at the level of the entero-anastomosis and four had to be killed because of persistent severe diarrhoea. Vital intestinal mucosa was found in all augmented bladders. There were no differences in bone length and volume. Loss of bone mass was almost exclusively in rats with ileocystoplasty and resection of the ileocaecal segment (-37.5%, pQCT, P < 0.01). There was no hyperchloraemic metabolic acidosis or gross impairment of renal function. Hypomagnesaemia, hypocalcaemia and decreased insulin-like growth factor-binding protein 3 were the only significant findings on blood analysis. Deoxypyridinoline crosslinks in urine were higher in rats with an enterocystoplasty than in controls.

CONCLUSIONS

Enterocystoplasty in rats neither impairs skeletal growth nor bone quantity, but leads to significant loss of bone mass when combined with resection of the ileocaecal segment. Rarefaction of the trabecular network is confined to the metabolically highly active cancellous compartment, most likely as a consequence of intestinal malabsorption.

Growth factor delivery for bone tissue engineering

Bone is a dynamic tissue that undergoes significant turnover during the life cycle of an individual. Despite having a significant regenerative capability, trauma and other pathological scenarios commonly require therapeutic intervention to facilitate the healing process. Bone tissue engineering, where cellular and biological processes at a site are deliberately manipulated for a therapeutic outcome, offers a viable option for the treatment of skeletal diseases. In this review paper, we aim to provide a brief synopsis of cellular and molecular basis of bone formation that are pertinent to current efforts of bone healing. Different approaches for engineering bone tissue were presented with special emphasis on the use of soluble (diffusible) therapeutic agents to accelerate bone healing. The latter agents have been used for both local bone repair (i.e. introduction of agents directly to a site of repair) as well as systemic bone regeneration (i.e. delivery for regeneration throughout the skeletal system). Critical drug delivery and targeting issues pertinent for each mode of bone regeneration are provided. In addition, future challenges and opportunities in bone tissue engineering are proposed from the authors' perspective.

Subcutaneous administration of insulin-like growth factor (IGF)-II/IGF binding protein-2 complex stimulates bone formation and prevents loss of bone mineral density in a rat model of disuse osteoporosis

Elevated serum levels of insulin-like growth factor binding protein-2 (IGFBP-2) and a precursor form of IGF-II are associated with marked increases in bone formation and skeletal mass in patients with hepatitis C-associated osteosclerosis. In vitro studies indicate that IGF-II in complex with IGFBP-2 has high affinity for bone matrix and is able to stimulate osteoblast proliferation. The purpose of this study was to determine the ability of the IGF-II/IGFBP-2 complex to increase bone mass in vivo. Osteopenia of the femur was induced by unilateral sciatic neurectomy in rats. At the time of surgery, 14-day osmotic minipumps containing vehicle or 2 microg IGF-II+9 microg IGFBP-2/100g body weight/day were implanted subcutaneously in the neck. Bone mineral density (BMD) measurements were taken the day of surgery and 14 days later using a PIXImus small animal densitometer. Neurectomy of the right hindlimb resulted in a 9% decrease in right femur BMD (P<0.05 vs. baseline). This loss in BMD was completely prevented by treatment with IGF-II/IGFBP-2. On the control limb, there was no loss of BMD over the 14 days and IGF-II/IGFBP-2 treatment resulted in a 9% increase in left femur BMD (P<0.05). Bone histomorphometry indicated increases in endocortical and cancellous bone formation rates and in trabecular thickness. These results demonstrate that short-term administration of the IGF-II/IGFBP-2 complex can prevent loss of BMD associated with disuse osteoporosis and stimulate bone formation in adult rats. Furthermore, they provide proof of concept for a novel anabolic approach to increasing bone mass in humans with osteoporosis.

Musculoskeletal effects of the recombinant human IGF-I/IGF binding protein-3 complex in osteoporotic patients with proximal femoral fracture: a double-blind, placebo-controlled pilot study

The administration of recombinant human IGF-I complexed with its predominant binding protein IGF binding protein-3 (rhIGF-I/IGFBP-3) may allow the safe administration of higher doses of IGF-I than can be accomplished with rhIGF-I alone. The aim of this randomized, double-blind, placebo- controlled pilot study was to evaluate the short-term safety and musculoskeletal effects of rhIGF-I/IGFBP-3 in older women (aged 65-90 yr) with recent hip fracture. Within 72 h after the event, 30 patients received continuous administration of either placebo (n = 10), 0.5 mg/kg.d rhIGF-I/IGFBP-3 (n = 9), or 1 mg/kg.d rhIGF-I/IGFBP-3 (n = 11). Treatment was administered by sc infusion through a portable mini-pump for a total of 8 wk after hip fracture surgery, with patient follow-up to 6 months after surgery. Efficacy evaluations included a contralateral hip bone density determination, markers of bone turnover (including serum osteocalcin and urinary excretion of N-telopeptide), grip strength, and tests of functional ability. During the administration of rhIGF-I/IGFBP-3, mean serum levels of IGF-I significantly (P < 0.001) increased from 83 ng/ml to 289 ng/ml (0.5 mg/kg.d) and 393 ng/ml (1 mg/kg.d), respectively. Both doses were well tolerated, and no hypoglycemia or other therapy-induced side effects were observed. After an initial loss of hip bone density after hip fracture surgery, patients treated with 1 mg/kg.d rhIGF-I/IGFBP-3 regained a substantial portion of their femoral bone mass. At 6 months postfracture (4 months after the 2-month infusion), they showed a statistically not significant decrease from baseline in hip bone density (-2.6%, P = 0.53). Placebo-treated patients, on the other hand, failed to regain lost bone: at 6 months postfracture, bone density in the placebo group had declined by 6.1% (P = 0.04). Additionally, in patients treated with 1.0 mg/kg.d rhIGF-I/IGFBP-3, grip strength had increased from baseline by 11.4% by the end of the study (P = 0.04) whereas patients on placebo lost 11.6% from baseline (P = 0.16). This increase in muscle strength in the high-dose group was associated with a positive effect on functional recovery. We conclude that a 2-month infusion of rhIGF-I/IGFBP-3 in patients with recent hip fracture is feasible, safe, and well tolerated. Analyzing the effects on bone mass, muscle strength, and functional ability, we observed beneficial trends. In the context of a small exploratory study, these findings should be interpreted with caution, but they support the need for future trials to further assess the therapeutic potential of rhIGF-I/IGFBP-3 in elderly subjects with osteoporosis.

The complex of recombinant human insulin-like growth factor-I (rhIGF-I) and its binding protein-5 (IGFBP-5) induces local bone formation in murine calvariae and in rat cortical bone after local or systemic administration

The influence of recombinant human insulin-like growth factor-I (rhIGF-I), its binding protein-5 (IGFBP-5) or their equimolar complexes on calvarial osteogenesis was investigated by quantitative radiography and histomorphometry after local administration to adult mice or mature rats. The systemic effects of these proteins were investigated in aged Sprague-Dawley rats with regard to their ability to prevent or restore bone mass in ovariectomy induced osteopenia as assessed by radiography, dual-energy X-ray absorptiometry (DEXA) analyses, peripheral computerized tomography (pQCT) and mineral analyses after daily s.c. administration for 3 or 8 weeks following a bone depletion period of 8 weeks. Bone mass of murine calvariae was significantly increased in a dose-dependent manner by the complex 7 days after discontinuation of local administration for 19 days in mice, whereas IGF-I alone expressed only weak effects. IGFBP-5 alone was ineffective in this respect. In the same model, only the complex had a weak osteogenetic potential in 7 week or 5 month old rats. Systemic long-term treatment with the complex of rhIGF-I/IGFBP-5 (2.0/7.6 mg/kg/day, s.c.) for 8 weeks resulted in significantly increased cortical thickness, area and mineral density in femoral midshaft or tibial metaphysis suggesting periosteal bone formation. This was obviously related to increased muscle strength since these effects were parallelled by increased body weight. No effect on trabecular bone occurred as demonstrated by site-specific analyses (vertebrae, proximal tibia) using DEXA, pQCT and radiography. This selective action of rhIGF-I/IGFBP-5 on periosteal bone formation is unique for an IGFBP. Femoral ash and calcium content, both corrected for tissue volume, increased slightly. However, when the increase in cortical thickness and bone mass was corrected for bone size, the effects are nearly abolished, suggesting an additional effect of bone growth. This potential deserves further evaluation in order to differentiate between effects on cortical bone via muscle strength and lack of efficacy on trabecular bone balance.

Bone anabolic effects of separate and combined therapy with growth hormone and parathyroid hormone on femoral neck in aged ovariectomized osteopenic rats

Previous studies have demonstrated that growth hormone (GH) has a marked anabolic effect on cortical bone and parathyroid hormone (PTH) has been shown to increase cancellous bone and cortical bone markedly in ovariectomized (OVX) rats. Most previous combination therapies used the bone anabolic agent (PTH) and the anti-resorptive agents. In this study, two bone anabolic hormones, GH and PTH, were used in rebuilding bone following loss due to ovariectomy in the femoral neck, which contains both cortical and cancellous bones. Twelve-month-old female F344 rats were divided into five groups: Sham+solvent vehicle, OVX+solvent vehicle, OVX+GH (2.5 mg/kg/day), OVX+PTH (80 microg/kg/day), and OVX+GH (2.5 mg/kg/day)+PTH (80 microg/kg/day). Following surgery, the animals were left for 4 months to become osteopenic before the beginning of hormone therapies. Hormone administrations were given 5 days per week for 2 months and the animals sacrificed. The right femurs were removed and the femoral necks were examined by pQCT densitometry and by histomorphometry. There was a 12.3% decrease in total bone mineral content (BMC) (P<0.01), a 6.2% decrease in total bone mineral density (BMD) (P<0.01), a 12.8% decrease in cortical BMC (P<0.05), a 25.9% decrease in cancellous BMC (P<0.0001), a 20.4% decrease in cancellous BMD (P<0.01), and a 34.2% decrease in cancellous bone volume (BV/TV) (P<0.0001) in vehicle-treated OVX rats. Growth hormone, PTH and GH+PTH treatment increased total BMC of the OVX rats by 14.4% (P<0.01), 23.5% (P<0.0001) and 30.6% (P<0.0001), respectively; increased total BMD by 7.0% (P<0.01), 9% (P<0.001) and 14.8% (P<0.0001), respectively; increased cortical BMC by 15.9% (P<0.05), 25.5% (P<0.001) and 29% (P<0.001), respectively; increased cancellous BMC by 40.9% (P<0.0001), 61.9% (P<0.0001) and 86.8% (P<0.0001), respectively; increased cancellous BMD by 31% (P<0.001), 41.8% (P<0.0001) and 61.8% (P<0.0001), respectively; increased cancellous BV/TV by 30.6% (P<0.05), 76.3% (P<0.0001) and 94.9% (P<0.0001), respectively; and increased trabecular thickness by 26.4% (P<0.05), 41.5% (P<0.001) and 43.2% (P<0.001), respectively, compared to the age-matched vehicle-treated OVX controls. In conclusion, both GH and PTH increased cortical and cancellous bone mass at the osteopenic femoral neck. Using two techniques, it was observed that the effects of PTH were mostly more marked than those of GH. Combined therapy with GH+PTH was more effective in rebuilding cortical bone and cancellous bone than either therapy alone in the aged ovariectomized osteopenic rats, which is in line with our hypothesis.

Inactivation of the acid labile subunit gene in mice results in mild retardation of postnatal growth despite profound disruptions in the circulating insulin-like growth factor system

Insulin-like growth factors (IGFs) I and II are important regulators of cell proliferation and differentiation. After birth, plasma IGFs, representing mostly liver-derived IGFs, circulate in ternary complexes of 150 kDa consisting of one molecule each of IGF, IGF-binding protein (IGFBP) 3, and an acid labile subunit (ALS). Onset of ALS synthesis after birth is the primary factor driving the formation of ternary complexes. Capture of IGFs by ALS is thought to allow the development of a plasma reservoir without negative effects such as hypoglycemia and cell proliferation. To evaluate the importance of ALS and ternary complexes, we have created mice in which the ALS gene has been inactivated. The mutation was inherited in a Mendelian manner, without any effects on survival rates and birth weights. A growth deficit was observed in null mice after 3 weeks of life and reached 13% by 10 weeks. This modest phenotype was observed despite reductions of 62 and 88% in the concentrations of plasma IGF-I and IGFBP-3, respectively. Increased turnover accounted for these reductions because indices of synthesis in liver and kidney were not decreased. Surprisingly, absence of ALS did not affect glucose and insulin homeostasis. Therefore, ALS is required for postnatal accumulation of IGF-I and IGFBP-3 but, consistent with findings supporting a predominant role for locally produced IGF-I, is not critical for growth. This model should be useful to determine whether presence of ALS is needed for other actions of liver-derived IGF-I and for maintenance of homeostasis in presence of high circulating levels of IGF-II.

Estrogen replacement therapy in the management of osteopenia related to eating disorders

The effect of hormone replacement therapy on the bone mineral content of hypoestrogenic subjects depends on the pathogenesis of the disease as well as on the dosage and route of administration. This is particularly true in hypoestrogenism related to eating disorders. We present a longitudinal study of 26 young women with diet-induced amenorrhea compared with a group of subjects with POF. The study protocol included the quantification of weight loss, the endocrine profile (follicle-stimulating hormone, luteinizing hormone, prolactin, E2, FT3, FT4, thyroid-stimulating hormone, and cortisol), the evaluation of markers of bone turnover (GLA, OSTK-PR, ALP, OHP, and DPYR), and spinal bone density by DEXA at observation and after weight recovery. No hormone replacement therapy was administered. Mean BMD and Z scores before and after recovery do not differ significantly; OHP and DPYR appear significantly higher during basal evaluation, whereas GLA and ALP do not. Data on the impact of oral contraceptive use on bone mineral density are controversial. We particularly discuss the question of long-term treatment with 20 micrograms ethinyl estradiol pills on peak bone mass acquisition during adolescence.

Selective drug delivery system to bone: small peptide (Asp)6 conjugation

Targeting a drug on hydroxyapatite (HA) could be a promising way for selective drug delivery to bone, because HA, an inorganic component in hard tissues (bone and teeth), does not exist in soft tissues. Several bone noncollagenous proteins, which bind to HA, have repeating sequences of acidic amino acids in their structures as possible HA-binding sites. Thus, we think that a small peptide of repetitive acidic amino acid could work as a carrier for selective drug delivery to the bone. To test this hypothesis, we conjugated (Asp)6 to fluorescein isothiocyanate (FITC), evaluated its affinity to HA in vitro, and examined its tissue distribution after injection into rats. Although fluorescein itself did not bind to HA, (Asp)6-FITC bound to HA as well as calceine and tetracycline. Twenty-four hours after intravenous injection of (Asp)6-FITC to rats, animals were killed, and ground sections of hard tissues and cryosections of soft tissues were made. Under a confocal laser scanning microscope, clear labeling lines were observed in bones and teeth, whereas no labeling was detected in soft tissues. In the rats administered with fluorescein alone, the fluorescent labeling was detected in neither hard nor soft tissues. Fluorescent analysis of blood, urine, and bones after (Asp)6-FITC administration revealed that biological half-life of FITC in blood was short (60 minutes) and that within 24 h, 95% of the administered FITC was excreted as urine whereas 2% of the FITC accumulated in bones. After subcutaneous administration of (Asp)6-FITC to mice, fluorescent intensity remaining in the femurs was measured periodically. In these mice the biological half-life of FITC in the femur was 14 days. Present results indicate that (Asp)6 is effective as a carrier for selective drug delivery to bone.

Effects of high-impact exercise on ultrasonic and biochemical indices of skeletal status: A prospective study in young male gymnasts

Physical activity has been proposed as one strategy to enhance bone mineral acquisition during growth. The aim of this study was to determine whether frequent impact loading associated with gymnastics training confers a skeletal benefit on pre- and peripubertal male gymnasts. We measured broadband ultrasonic attenuation (BUA, dB/MHz) at the calcaneus (CBUA); ultrasound velocity (m/s) at the calcaneus (CVOS), distal radius (RVOS) and phalanx (PVOS); serum osteocalcin (OC); total alkaline phosphatase (ALP) and insulin-like growth factor-I (IGF-I) every 3-4 months over an 18-month period in elite male gymnasts and matched normoactive controls (pubertal stage </=2). Ground reaction forces of common gymnastics maneuvers were determined using a force platform and loading histories of the upper and lower extremities approximated from video recordings. Ultrasound results were expressed as a standardized score (Z score) adjusted for age, height, and weight. At baseline, no differences were detected between the gymnasts (n = 31) and controls (n = 50) for CBUA, although ultrasound velocity at each site was higher in the gymnasts (0.6-1.5 SD) than the predicted mean in controls (p </= 0. 001). Over 18 months, CBUA Z scores increased significantly in the gymnasts from baseline (0.3 vs. 1.0, p < 0.05, n = 18). In contrast, ultrasound velocity did not increase in either group, although CVOS and RVOS remained significantly higher in gymnasts compared with controls (range p < 0.01 and < 0.001). No differences between groups were found for OC, ALP, or IGF-I at any time. Gymnastics training was associated with on average 102 and 217 impacts per session on the upper and lower extremities, respectively, with peak magnitudes of 3.6 and 10.4 times body weight. These results suggest that frequent high-impact, weight-bearing exercise during the pre and peripubertal period may enhance the mechanical competence of the skeleton, perhaps offering an important strategy for osteoporosis prevention if the benefits are maintained.

Histomorphometric, physical, and mechanical effects of spaceflight and insulin-like growth factor-I on rat long bones

Previous experiments have shown that skeletal unloading resulting from exposure to microgravity induces osteopenia in rats. In maturing rats, this is primarily a function of reduced formation, rather than increased resorption. Insulin-like growth factor-I (IGF-I) stimulates bone formation by increasing collagen synthesis by osteoblasts. The ability of IGF-I to prevent osteopenia otherwise caused by spaceflight was investigated in 12 rats flown for 10 days aboard the Space Shuttle, STS-77. The effect IGF-I had on cortical bone metabolism was generally anabolic. For example, humerus periosteal bone formation increased a significant 37.6% for the spaceflight animals treated with IGF-I, whereas the ground controls increased 24.7%. This increase in humeral bone formation at the periosteum is a result of an increased percent mineralizing perimeter (%Min.Pm), rather than mineral apposition rate (MAR), for both spaceflight and ground control rats. However, IGF-I did inhibit humerus endocortical bone formation in both the spaceflight and ground control rats (38.1% and 39.2%, respectively) by limiting MAR. This effect was verified in a separate ground-based study. Similar histomorphometric results for spaceflight and ground control rats suggest that IGF-I effects occur during normal weight bearing and during spaceflight. Microhardness measurements of the newly formed bone indicate that the quality of the bone formed during IGF-I treatment or spaceflight was not adversely altered. Spaceflight did not consistently change the structural (force-deflection) properties of the femur or humerus when tested in three-point bending. IGF-I significantly increased femoral maximum and fracture strength.

Potential role of insulinlike growth factors in fracture healing

Several lines of evidence suggest that the insulinlike growth factors play a role in fracture healing. They promote cell proliferation and matrix synthesis by chondrocytes and osteoblasts, the two cell types largely responsible for the formation of fracture callus. Circulating levels of insulinlike growth factor I and bone mineral density decrease with increasing age, and administration of insulinlike growth factor I increases bone turnover in patients with low bone mineral density. Insulinlike growth factor I may accelerate the normal healing of intramembranous bone defects, inducing the healing of defects that otherwise would not heal. An important role of insulinlike growth factor I is to mediate many of the actions of growth hormone on the skeleton. Considerable effort has been devoted to testing the effect of growth hormone and, thereby, indirectly that of insulinlike growth factor I on fracture healing. These studies have yielded such disparate results that no general conclusions regarding the effect of growth hormone (or of growth hormone dependent insulinlike growth factor I) on fracture healing currently can be drawn. Additional studies are needed to clarify the role of the insulinlike growth factors in the fracture healing process and to determine how their anabolic actions can be enlisted in the clinical enhancement of fracture healing.

Clodronate prevents osteopenia and loss of trabecular connectivity in estrogen-deficient rats

Daily oral clodronate treatment was evaluated in Sprague-Dawley rats for its ability to inhibit estrogen-deficiency-induced changes in femoral neck, femoral diaphysis, and lumbar vertebrae (L4-L5). Six-month-old ovariectomized (OVX) rats were administered by gavage a vehicle (Veh) or clodronate (100 or 500 mg/kg/day). Sham-operated (SHAM) control rats received the vehicle (n = 15/group). Treatment was started on the day of operation and continued for 3 months. Trabecular bone volume (BV/TV) and structural variables (trabecular number, Tb.N; thickness, Tb.Th; separation, Tb.Sp; and trabecular bone pattern factor, Tb.Pf) were assessed on secondary spongiosa of the right femoral neck Furthermore, cantilever bending test of the left femoral neck and compression test of L4, ash weight of L5, and morphometric studies of femoral diaphysis were carried out, and serum and urinary markers of bone turnover were determined. The OVX/Veh group had higher levels of serum osteocalcin and alkaline phosphatase and higher urinary excretion of deoxypyridinoline/creatinine than the SHAM/Veh group at 3 months postsurgery, and clodronate reduced these changes. BV/TV of femoral neck, bone mass of L5, and the maximum loads of the femoral neck and L4 were lower after OVX than SHAM operation. Although clodronate prevented trabecular bone loss in the femoral neck and preserved Tb.Pf at the SHAM control level, it failed to preserve the mechanical strength at the femoral neck However, in lumbar vertebrae, clodronate prevented the loss of bone mass and mechanical properties. Furthermore, there was a good positive correlation between maximum load of L4 and the ash weight of L5 (n = 58, r = 0.69, p < 0.001). In the femoral neck (n = 55), Tb.Pf correlated negatively with BV/TV and Tb.N (r = -0.59 and r = -0.55;p < 0.001, respectively) and positively with Tb.Sp (r = 0.61, p < 0.001). In femoral mid-diaphysis, there were no significant changes in cortical bone geometry in any of the groups. We conclude that orally administered clodronate suppresses the enhanced bone turnover in adult OVX rats and preserves trabecular bone volume and connectivity in the femoral neck In the axial skeleton, clodronate has a beneficial effect on lumbar vertebral bone mass and strength.

Morphological and structural characteristics of the proximal femur in human and rat

Because the ovariectomized rat model of postmenopausal osteoporosis is the most commonly used small animal model to investigate consequences of bone loss on bone structure and strength, or to assess benefits of the various therapeutic strategies to improve bone mass and strength, the attempt was made to compare histoanatomical and structural characteristics of the femoral neck between human and rat models. In addition to different biomechanics, there is a significant difference in gross- and microanatomy of the proximal femur between humans and rats. Percent of the cortical bone component is much higher in rats (72.5%) relative to humans (12.5%). Also, cortical bone at the femoral neck in rats is evenly distributed, whereas in humans there is a considerable difference in the amount of the cortical bone between the superior half of the femoral neck with cortical thickness being only 0.3 mm, and the inferior half of the neck having 6-mm-thick cortex. Humans have far more cancellous bone at the femoral neck (22.7% average) relative to rats (6.8%). In addition, cancellous bone at the femoral neck in humans is unevenly distributed between the bone center and its periphery. Human samples exhibited striking differences in the cancellous bone structure between weight-bearing and tensile trabecular groups exhibiting clear trabecular orientation consisting of plates and rods, and trabeculae around the neutral bone axis with little mechanical activity exhibiting rod-like trabeculae only. Although humans and rats have a periosteum covering the femoral neck, and each lacks the muscular attachment at intracapsular portions of the femoral neck, rats, in contrast to humans, have the ability to quickly adapt cortical thickness and increase inertia to meet mechanical needs via modeling-dependent periosteal apposition.

Time course of femoral neck osteopenia in ovariectomized rats

To characterize osteopenic changes in the femoral neck of ovariectomized (ovx) rats, female Sprague-Dawley rats were ovx or sham operated upon at 3 months of age and killed at various times from 0 to 360 days postsurgery. Quantitative bone histomorphometry was performed on undecalcified longitudinal sections of the proximal femur from each rat. This skeletal site was found to be slowly growing, as its rate of longitudinal bone growth in 3-month-old baseline control rats (5 microns/day) was nearly a factor of 10 less than that of a more commonly used sample site, the proximal tibia. In control rats, cancellous bone volume and cortical bone width of the femoral neck remained relatively constant, but cancellous mineral apposition rate declined with age during the course of the study. In contrast, cancellous bone volume in ovx rats was significantly decreased to 75%-82% of control level at 30-90 days and further decreased to 50%-56% of control level at later times postovariectomy. Indices of cancellous bone turnover such as osteoclast and osteoblast surfaces and bone formation rate were markedly increased in ovx rats at 30 days, declined toward control levels by 90 days, then increased moderately at 180-360 days. In comparison to control rats, a slight decrease in cortical width of the femoral neck was observed in ovx rats at 180 days and reached statistical significance at 360 days postovariectomy. Endocortical bone formation rate was increased significantly in ovx rats compared with control rats at most time points. The results indicate that both cancellous and cortical osteopenia associated with high bone turnover occur in the femoral neck of ovx rats. Cancellous bone loss at this skeletal site is statistically significant as early as 30 days postovariectomy, but remains relatively moderate for the first 90 days before becoming more pronounced at later times after ovariectomy. In contrast, cortical osteopenia was not observed in the femoral neck of ovx rats until 1 year postovariectomy. This histomorphometric characterization of osteopenic changes in the femoral neck of ovx rats may serve as a basis for use of this slowly growing sample site in preclinical studies of the prevention and treatment of bone loss in the estrogen-depleted skeleton.

Histo-anatomy of the proximal femur in rats: impact of ovariectomy on bone mass, structure, and stiffness

BACKGROUND

Hip fractures are the most devastating consequence of osteoporosis in humans. Since the ovariectomized (ovx) rat is a useful model of estrogen-deficient osteoporosis, the purposes of this study were to describe the histo-anatomical features of the rat hip and to determine changes in the proximal femur induced by ovariectomy to evaluate the use of this skeletal site for future bone studies.

METHODS

Changes in body mass and composition and in bone mineral content and density were determined by DEXA at 12 weeks after ovariectomy. Gross and histo-anatomy of the rat hip was studied by light microscopy and histomorphometry. Cancellous and cortical bone changes induced by ovx at the femoral midneck were determine using dynamic, static, and structural histomorphometric techniques. The stiffness of the femoral neck was determined by biomechanical testing, and the results were correlated with histological observations and the histomorphometric data.

RESULTS

The bony structures of the rat hip, articular cartilage, and muscular and capsular attachments are very similar to the human. Rats, however, have an active growth plate and a well-vascularized periosteum covering the intracapsular portion of the femoral neck, which is different from the adult humans. Rats in the sham and ovx groups exhibited similar biological variations in the thickness of the femoral neck and epiphyseal bone and cartilaginous composition. Ovariectomy promoted periosteal modeling and induced endocortical and cancellous bone remodeling, with a net loss of bone mass due to excess bone resorption. The ovx-induced increase in resorption resulted in reduced trabecular number, thickness, and endocortico-trabecular connectivity, which likely contributed to less bone stiffness in ovx rats relative to the sham controls.

CONCLUSIONS

There are numerous similarities in the structure and histology of the rodent and human hip. Skeletal changes induced by ovariectomy in rats, particularly those at the endocortical surface and in the cancellous bone, are very similar to changes observed in the proximal femur in osteoporotic women. In addition, ovx in the rat had compromised the biomechanical properties at the femoral neck, similar to what occurs in the postmenopausal women. Data presented here confirmed responsiveness of the proximal femur in rat to ovarian hormone deficiency, which appears to be a useful and relevant site to investigate mechanisms and interventions relative to human disease.

Metabolic effects of recombinant human insulin-like growth factor-I in humans: comparison with recombinant human growth hormone

Many of the metabolic actions of growth hormone (GH) are mediated through insulin-like growth factors or somatomedins. Recombinant human insulin-like growth factor-I (rhIGF-I) has a dichotomous insulin-like and GH-like action when used in different clinical situations in humans. Its effects on carbohydrate metabolism show a prominent increase in total insulin sensitivity, causing hypoglycemia in higher doses and maintaining normal glucose homeostasis in lower doses. This polypeptide selectively stimulates whole body protein synthesis with no effect on proteolysis when given in doses of 100 micrograms/ kg subcutaneously twice daily for at least 5-7 days, effects which are indistinguishable from those of GH. This contrasts with the marked suppression of proteolysis observed when higher doses are given, similar to the effects observed with insulin. When used in combination with rhGH, rhIGF-I has a synergistic effect, improving total nitrogen retention in calorically deprived subjects, yet it does not cause any greater enhancement of whole body protein anabolism in normally fed volunteers than giving rhGH and rhIGF-I individually. This suggests a common pathway for IGF-I and GH enhancing protein anabolism in the normally fed state. rhIGF-I also stimulates linear growth in children with defects in the GH receptor. Recent data show that this potent growth factor has a potential advantage over GH in the treatment of severe protein catabolic states, particularly the glucocorticosteroid-dependent model, as it ameliorates the marked increase in protein catabolism caused by the steroids, but without a diabetogenic effect. Here, a brief overview is provided of available human data on the actions of this peptide on carbohydrate, lipid, and protein metabolism, linear growth, and its anabolic effects. rhIGF-I offers promise in the treatment of selective growth disorders and in protein catabolic and insulin-resistant states.

Co-administration of IGF-binding protein-3 differentially inhibits the IGF-I-induced total body and organ growth of Snell dwarf mice

In mammals IGF-I is part of a 150-kDa binding protein complex, which also contains a glycosylated acid-labile protein (ALS) and a glycosylated acid-stable IGF binding subunit IGFBP-3. Administration of free IGF-I in vivo induces not only acute insulin-like effects but also growth stimulation. Since co-injection with IGFBP-3 only partially blocked the hypoglycemic response of free IGF-I in hypophysectomized rats, we were interested in the growth stimulating activity of the IGFI-IGFBP-3 complex in pituitary-deficient mice compared to that obtained by IGF-I alone. Therefore, the effects of subcutaneously administered IGF-I, IGFBP-3 and the IGF-I-IGFBP-3 complex on somatic growth and organ growth of pituitary-deficient Snell dwarf mice were studied after 4 weeks of treatment. Treatment with IGF-I alone induced a significant increase in body length and weight, as well as in weights of the submandibular salivary glands, kidneys and quadriceps femoris muscles as compared to buffer treated controls. No significant changes were found in liver, brain, heart and thymus. IGFBP-3 alone had no effect. However, the stimulating effects of IGF-I alone on body length and weight, as well as on the weight of the kidneys, were fully neutralized by co-injection with IGFBP-3. In contrast, the weights of submandibular salivary glands and m. quadriceps femoris were increased by treatment with the complex compared to controls and not significantly different from animals treated with IGF-I alone. Our data show that in GH-deficient mice administration of IGFBP-3 differentially inhibits the IGF-I induced body and organ growth. This calls for extra vigilance when exploring presumed advantages of administering an IGF-I-IGFBP-3 complex to GH-deficient individuals in order to obtain stimulation of growth.