The influence of combined parathyroid hormone and growth hormone treatment on cortical bone in aged ovariectomized rats

Trehalose enhances bone fracture healing in a rat sleep deprivation model

Background

The purpose of this study was to investigate whether sleep deprivation (SD) could delay bone fracture healing and evaluate the therapeutic effect of trehalose.

Methods

Eighteen 300-350 g female Sprague-Dawley rats were created a mid-femoral transverse osteotomy in the right thigh and divided into three groups (i.e., group 1: fracture; group 2: fracture + SD; and group 3: fracture + SD + trehalose). Seven days after surgery, the rats in group 2 and group 3 were started to get sleep-deprived for 18 h per day for 3 weeks. The rats in group 3 were injected with trehalose intraperitoneally at 1 g/kg/d for 3 weeks. Radiological and histological analyses were used to assess fracture healing quality. Circulating cytokines were detected by the end of the study. The expression of M1 and M2 macrophage markers were measured by quantitative real-time polymerase chain reaction (qPCR).

Results

X-rays showed group 2 experienced much poorer fracture healing. Micro CT demonstrated that the bone quality of the fracture callus site in group 2 was much worse than that in groups 1 and 3. Both haematoxylin eosin (H&E) and Masson staining revealed that the bone fracture of the group 2 healed worse. Elisa results demonstrated that the interleukin-1 beta (IL-1β) and tumor necrosis factor-alpha (TNF-α) of the rats in group 2 were significantly higher. In vitro study showed that 100 mM trehalose enhanced the expression of M2 macrophage markers (Arg-1 and IL-10), and decreased M1 macrophage polarization through the decreasing expression of IL-6.

Conclusions

The present study showed (SD) could delay bone fracture healing in a rat model. And, trehalose could promote the healing of delayed bone fracture union by down-regulating pro-inflammatory mediators and enhancing M2 polarization.

Bone Measurements by Peripheral Quantitative Computed Tomography in Rodents

This chapter provides information for the in vivo use of peripheral quantitative computed tomography in rats and mice to determine bone density and cortical geometric data, including suggestions for study design, instrument setting, and data interpretation. This update also provides guidance for the use of pQCT to extract muscle and fat cross-sectional area information from the bone scans.

PTH (1-34) and growth hormone in prevention of disuse osteopenia and sarcopenia in rats

Osteopenia and sarcopenia develops rapidly during disuse. The study investigated whether intermittent parathyroid hormone (1-34) (PTH) and growth hormone (GH) administered alone or in combination could prevent or mitigate disuse osteopenia and sarcopenia in rats. Disuse was achieved by injecting 4IU botulinum toxin A (BTX) into the right hindlimb musculature of 12-14-week-old female Wistar rats. Seventy-two rats were divided into six groups: 1. Baseline; 2. Ctrl; 3. BTX; 4. BTX+GH; 5. BTX+PTH; 6. BTX+PTH+GH. PTH (1-34) (60μg/kg/day) and GH (5mg/kg/day). The animals were sacrificed after 6weeks of treatment. Sarcopenia was established by histomorphometry, while the skeletal properties were determined using DXA, μCT, mechanical testing, and dynamic bone histomorphometry. Disuse resulted in lower muscle mass (-63%, p<0.05), trabecular BV/TV (-28%, p<0.05), Tb.Th (-11%, p<0.05), lower diaphyseal cortical thickness (-10%, p<0.001), and lower bone strength at the distal femoral metaphysis (-27%, p<0.001) compared to Ctrl animals. PTH fully counteracted the immobilization-induced lower BV/TV, Tb.Th, and distal femoral metaphyseal strength. GH increased muscle mass (+17%, p<0.05) compared to BTX, but did not prevent the immobilization-induced loss of bone strength, BV/TV, and cortical trabecular thickness. Combination of PTH and GH increased distal femoral metaphyseal bone strength (+45%, p<0.001), BV/TV (+50%, p<0.05), Tb.Th (+40%, p<0.05), and whole femoral aBMD (+15%, p<0.001) compared to BTX and muscle mass (+21%, p<0.05) compared to BTX+PTH. In conclusion, PTH and GH in combination is more efficient at preventing the disuse-related deterioration of bone strength, density, and micro-architecture than either PTH or GH given as monotherapy. Furthermore, GH, either alone or in combination with PTH, attenuated disuse-induced loss of muscle mass. The combination of PTH and GH resulted in a more effective treatment than PTH and GH as monotherapy.

Effects of combined teriparatide and zoledronic acid on posterior lumbar vertebral fusion in an aged ovariectomized rat model of osteopenia

There has been no study regarding the effect of a combination of teriparatide (TPTD) and zoledronic acid (ZA) on vertebral fusion. In this study, we investigate the effect of single and combined TPTD and ZA treatment on lumbar vertebral fusion in aged ovariectomized (OVX) rats. Sixty two-month-old female Sprague-Dawley rats were ovariectomized and underwent bilateral L4-L5 posterolateral intertransverse fusion after 10 months. The OVX rats received vehicle (control) treatment, or ZA (100 µg/kg, once), or TPTD (60 µg/kg/2 d for 42 d), or ZA + TPTD until they were euthanized at 6 weeks following lumbar vertebral fusion. The lumbar spine was harvested. Bone mineral density (BMD), bone fusion, bone volume (BV), and bone formation rate (BFR)were analyzed by dual-energy X-ray absorptiometry (DXA), radiography, micro-computed tomography, and histomorphometry. Compared with vehicle (control) treatment, ZA and TPTD monotherapy increased bone volume (BV) at fusion site, and ZA + TPTD combined therapy had an additive effect. Treatment with TPTD and ZA + TPTD increased the bone fusion rate when compared with the control group. ZA monotherapy did not alter the rate of bone fusion. The TPTD and ZA + TPTD treatment groups had increased mineral apposition rate (MAR), mineralizing surfaces/bone surface ((MS/BS), and BFR/BS compared with the OVX group. Our experiment confirm that the monotherapy with TPTD and combination therapy with ZA + TPTD in an OVX rat model of osteopenia following lumbar vertebral fusion surgery increased bone fusion mass and bone fusion rate, and ZA + TPTD combined therapy had an additive effect on bone fusion mass. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:937-944, 2018.

Effects of chronic sleep deprivation on bone mass and bone metabolism in rats

BACKGROUND

This study aimed to assess the effects of chronic sleep deprivation (CSD) on bone mass and bone metabolism in rats.

METHODS

Twenty-four rats were randomly divided into CSD and control (CON) groups. Rats were subjected to CSD by using the modified multiple platform method (MMPM) to establish an animal model of CSD. Biochemical parameters such as levels of serum N-terminal propeptide of type I procollagen (PINP), N-terminal cross-linking telopeptide of type I collagen (NTX), growth hormone (GH), estradiol (E2), serum 25(OH)D, and calcium (Ca) were evaluated at 0, 1, 2, and 3 months. After 3 months, each fourth lumbar vertebra and the distal femoral metaphysis of the left extremity of rats were harvested for micro-computed tomography scans and histological analysis, respectively, after the rats were sacrificed under an overdose of pentobarbital sodium.

RESULTS

Compared with rats from the CON group, rats from the CSD group showed significant decreases in bone mineral density (BMD), bone volume over total volume, trabecular bone thickness, and trabecular bone number and significant increases in bone surface area over bone volume and trabecular bone separations (P < 0.05). Bone histomorphology studies showed that rats in the CSD group had decreased osteogenesis, impaired mineralization of newly formed bones, and deteriorative trabecular bone in the secondary spongiosa zone. In addition, they showed significantly decreased levels of serum PINP (1 month later) and NTX (3 months later) (P < 0.05). The serum 25(OH)D level of rats from the CSD group was lower than that of rats from the CON group after 1 month (P < 0.05).

CONCLUSIONS

CSD markedly affects bone health by decreasing BMD and 25(OH)D, deteriorating the bone microarchitecture, and decreasing bone formation and bone resorption markers.

Intermittent Administration of Parathyroid Hormone [1-34] Prevents Particle-Induced Periprosthetic Osteolysis in a Rat Model

We examined whether intermittent administration of parathyroid hormone [1-34] (PTH[1-34]; 60 μg/kg/day) can prevent the negative effects of titanium (Ti) particles on implant fixation and periprosthetic osteolysis in a rat model. Eighteen adult male rats (12 weeks old, bones still growing) received intramedullary Ti implants in their bilateral femurs; 6 rats from the blank group received vehicle injections, and 12 rats from the control group and PTH treatment group received Ti particle injections at the time of operation and intra-articular injections 2 and 4 weeks postoperatively. Six of the rats that received Ti particles from the PTH group also received PTH[1-34] treatment. Six weeks postoperatively, all specimens were collected for assessment by X-ray, micro-CT, biomechanical, scanning electron microscopy (SEM), and dynamic histomorphometry. A lower BMD, BV/TV, Tb.N, maximal fixation strength, and mineral apposition rate were observed in the control group compared to the blank group, demonstrating that a periprosthetic osteolysis model had been successfully established. Administration of PTH[1-34] significantly increased the bone mineral density of the distal femur, BV/TV, Tb.N, Tb.Th, Tb.Sp, Con.D, SMI, and maximal fixation strength in the PTH group compared to that in the control group. SEM revealed higher bone-implant contact, thicker lamellar bone, and larger trabecular bone area in the PTH group than in the control group. A higher mineral apposition rate was observed in the PTH group compared to both the blank and control groups. These findings imply that intermittent administration of PTH[1-34] prevents periprosthetic osteolysis by promoting bone formation. The effects of PTH[1-34] were evaluated at a suprapharmacological dosage to the human equivalent in rats; therefore, additional studies are required to demonstrate its therapeutic potential in periprosthetic osteolysis.

PTH (1-34), but not strontium ranelate counteract loss of trabecular thickness and bone strength in disuse osteopenic rats

PTH and strontium ranelate (SrR) have both been shown to reduce bone loss induced by immobilization. PTH is a potent bone anabolic agent, whereas SrR has been suggested to be an antiresorptive as well as a bone anabolic agent. The aim of the study was to investigate whether PTH, SrR, and PTH and SrR in combination could counteract immobilization-induced bone loss in a rat model. Immobilization was induced by injecting 4IU Botox (BTX) into the muscles of the right hind limb. Seventy-two female Wistar rats, 3-months-old, were divided into the following groups: Baseline, Controls, BTX, BTX+PTH, BTX+SrR, and BTX+PTH+SrR (n=12 in each group). PTH was given as injections (SC) at a dosage of 60μg/kg/d, and SrR as 900mg/kg/d in the diet. The experiment lasted for 4weeks. BTX resulted in lower trabecular bone formation rate (-68%) and periosteal bone formation rate (-91%), and a higher fraction of osteoclast-covered surfaces (+53%) compared with controls. This was accompanied by significantly lower trabecular bone volume fraction (-24%), trabecular thickness (-16%), and bone strength (-14% to -32% depending on site). PTH alone counteracted immobilization-induced losses in trabecular (4-fold increase vs. BTX) and periosteal (5-fold increase vs. BTX) bone formation rate, trabecular thickness (+25% vs. BTX) and femoral neck strength (+24% vs. BTX). In contrast, SrR did not influence BTX-induced loss of bone formation rate, trabecular bone volume fraction, trabecular thickness, or bone strength. Finally, no additive effect was found when PTH and SrR treatments were combined. In conclusion, PTH counteracted loss in bone architecture and bone strength in immobilized rats, whereas as no effect of SrR was found. Moreover, no additional effect was found by combining PTH with SrR.

Bone measurements by peripheral quantitative computed tomography in rodents

This chapter provides information for the use of peripheral quantitative computed tomography in small animals, including suggestions for study design, instrument setting, and data interpretation.

Strontium ranelate enhances callus strength more than PTH 1-34 in an osteoporotic rat model of fracture healing

Treatment of an underlying disease is often initiated after the occurrence of an osteoporotic fracture. Our aim was to investigate whether teriparatide (PTH 1-34) and strontium ranelate affect fracture healing in ovariectomized (OVX) rats when provided for the first time after the occurrence of an osteoporotic fracture. We combined the model of an OVX rat with a closed diaphyseal fracture. Sixty Sprague Dawley rats were randomly assigned to four groups. Fracture healing in OVX rats after treatment with pharmacological doses of strontium ranelate and PTH 1-34 was compared with OVX and sham-treated control groups. After 28 days, the femur was excised and scanned by micro computed tomography and the callus evaluated, after which biomechanical torsional testing was performed and torque and toughness until reaching the yield point were analyzed. Only treatment with strontium ranelate led to a significant increase in callus resistance compared to the OVX control rats, whereas both PTH 1-34 and strontium ranelate increased the bone volume/tissue volume ratio of the callus. The PTH 1-34-increased trabecular bone volume within the callus was even higher compared to sham. As for the callus tissue volume, the increase induced by strontium ranelate was significant, contrary to the changes induced by PTH. Callus in strontium ranelate-treated animals is more resistant to torsion compared with OVX control rats. To our knowledge, this is the first report of the enhancement of fracture healing by strontium ranelate. Because both treatments enhance bone and tissue volume within the callus, there may be a qualitative difference between the calluses of PTH 1-34- and strontium ranelate-treated OVX rats. The superior results obtained with strontium ranelate compared to PTH in terms of callus resistance could be the consequence of a better quality of the new bone formed within the callus.

Factors associated with elevated or blunted PTH response in vitamin D insufficient adults

OBJECTIVES

The purpose of this study was to examine factors associated with high or low parathyroid hormone (PTH) levels in relationship to vitamin D insufficiency.

DESIGN

This was a cross-sectional study consisting of 516 healthy men and women, aged 30-85, all Caucasians with vitamin D insufficiency [serum 25(OH)D<45 nmol L(-1)]. The group was divided into quartiles by PTH levels and the highest and lowest quartiles were compared with regard to various factors likely to affect calcium metabolism. We used stepwise multivariable logistic regression to determine the independent association between PTH levels and other variables for men and women separately.

RESULTS

We found that men in the lowest PTH quartile were significantly younger, had less energy intake, lower body mass index (BMI) and better kidney function compared with the highest PTH quartile. They had also higher ionized calcium, insulin-like growth factor (IGF1) and testosterone and were more likely to smoke. Women within the lowest PTH quartile were younger, had lower BMI and magnesium values and higher IGF1 levels and were more likely to smoke. Stepwise multivariate regression showed that IGF1, testosterone and BMI were significantly associated with PTH in men (R(2)=0.472) but smoking, BMI and kidney function in women (R(2)=0.362).

CONCLUSIONS

Our results indicate that during vitamin D insufficiency, factors other than calcium and vitamin D may modify PTH response. These factors may be different between sexes and we have identified novel factors, IGF1 and testosterone in men which may be compensatory in nature and confirmed previous factors such as smoking, BMI and kidney function in women.

Biomechanical testing in experimental bone interventions--May the power be with you

Total variation in any measured variable, in conjunction with expected treatment effect, defines the minimum sample size (minSS) required to detect the expected effect with statistical confidence should the effect truly exist. A comprehensive literature survey of 3472 original studies was carried out to identify studies with biomechanical testing of whole bones. Total variation in common biomechanical traits and expected treatment effects in typical interventions were statistically determined. According to this survey, total variation in biomechanical traits between different species of experimental animals was similar, justifying the use of rat femur as a model in further analyses. Due to poorer precision, stiffness and energy absorption assessment require substantially larger sample size than breaking load. Due to same reason, minSS for femoral neck compression test is considerably larger than for femoral shaft three-point bending test. For the bending test, minSS to show a 10% treatment effect in the breaking load with 80% statistical power is 11rats/group, while corresponding minSS is 23 for the stiffness, and 53 for the energy absorption. For the femoral neck compression test, minSSs are 16, 51, and 134rats/group, respectively. Among the reviewed studies, the mean sample size was 11animals/group. This underscores the need for considerably larger sample sizes in experimental bone interventions which employ mechanical traits as primary outcome variables. In particular, poor precision and generally small expected treatment effects compromise the utility of stiffness and energy absorption assessments in experimental bone interventions.

Intermittently administered parathyroid hormone 1-34 reverses bone loss and structural impairment in orchiectomized adult rats

Male osteoporosis is emerging as a central theme in bone research. As in females, hypogonadism appears as a principal risk factor in men that leads to bone loss and increased fracture incidence. Intermittently administered parathyroid hormone (PTH) reverses bone loss in sex hormone-deprived women and female animals and increases bone mass in elderly men and normal male animals. This study was carried out to assess whether the PTH anabolic activity is also effective in adult castrated males and to gain insight into the underlying tissue processes. Bilateral orchiectomy (ORX) or sham-ORX was performed in 13-week old rats. Five weeks later, the ORX rats were treated intermittently with human PTH(1-34), 80 microg/kg/day or vehicle for 6 weeks. Femora were evaluated by quantitative micro-computed tomography followed by dynamic histomorphometry. The trabecular bone volume density showed 40% and 56% ORX-induced loss in the distal metaphysis at 6 weeks and 12 weeks post-ORX, respectively. PTH(1-34) induced supraphysiologic recovery of this bone loss (155% recovery) consequent to a vast increase in trabecular thickness (174% over sham-ORX controls) and a partial reversal (62%) of the decrease in trabecular number. As compared with the results in 12-week, orchiectomized vehicle-administered rats, the PTH(1-34) treatment induced a significant decrease in osteoclast number (20%) and twofold increase in bone formation rate. While ORX did not affect the femoral diaphysis, PTH(1-34) induced marked cortical thickening via the stimulation of endosteal mineral appositional rate (154% over ORX rats). These data portray PTH(1-34) as a highly potent bone anabolic agent in adult ORX rats, mainly by increasing both the trabecular and cortical thicknesses through its effect on osteoblasts and osteoclasts. The adult ORX rat is useful for investigating the processes involved in bone anabolic activity in castrated osteoporotic males and for the development of bone anabolic agents for treating this condition.

Growth hormone cannot enhance the recovery of dexamethasone-induced osteopenia after withdrawal in young female wistar rats

Dexamethasone (DEX) suppresses the secretion of and responsiveness to growth hormone (GH). Here we aimed to assess the therapeutic effects of GH on the DEX-induced osteopenia. Female Wistar rats were treated for 2 weeks with DEX (200 microg/day) or saline as a control. DEX significantly decreased body weight gain, bone mineral density (BMD), growth plate thickness, area ratio of trabecular bone, and serum osteocalcin levels. DEX also elongated the tibia primary spongiosa and caused many tiny lipid droplets in the tibia marrow. These results indicated that DEX induced osteopenia in rats. We then assessed the effects of GH on the recovery of osteopenia after withdrawal of DEX. DEX-treated rats were subsequently treated for 1 week with GH (0.1 or 0.3 U/day) or saline, while saline-pretreated rats were treated for 1 week with saline as a control. GH (0.1 or 0.3 U/day)-treated rats showed a catch-up growth in various bone measurements by one week after DEX withdrawal, though most of them remained subnormal. GH treatment did not enhance the recovery of DEX-induced osteopenia. Therefore a short-term exposure to DEX significantly impaired the bone metabolism, which started to recover soon after withdrawal of DEX. Unfortunately, immediate administration of GH after withdrawal of DEX did not enhance the recovery process.

Response of induced bone defects in horses to collagen matrix containing the human parathyroid hormone gene

OBJECTIVE

To determine whether human parathyroid hormone (hPTH) gene in collagen matrix could safely promote bone formation in diaphyseal or subchondral bones of horses.

ANIMALS

8 clinically normal adult horses.

PROCEDURE

Amount, rate, and quality of bone healing for 13 weeks were determined by use of radiography, quantitative computed tomography, and histomorphometric analysis. Diaphyseal cortex and subchondral bone defects of metacarpi were filled with hPTH(1-34) gene-activated matrix (GAM) or remained untreated. Joints were assessed on the basis of circumference, synovial fluid analysis, pain on flexion, lameness, and gross and histologic examination.

RESULTS

Bone volume index was greater for cortical defects treated with hPTH(1-34) GAM, compared with untreated defects. Bone production in cortical defects treated with hPTH(1-34) GAM positively correlated with native bone formation in untreated defects. In contrast, less bone was detected in hPTH(1-34) GAM-treated subchondral bone defects, compared with untreated defects, and histology confirmed poorer healing and residual collagen sponge.

CONCLUSIONS AND CLINICAL RELEVANCE

Use of hPTH(1-34) GAM induced greater total bone, specifically periosteal bone, after 13 weeks of healing in cortical defects of horses. The hPTH(1-34) GAM impeded healing of subchondral bone but was biocompatible with joint tissues. Promotion of periosteal bone formation may be beneficial for healing of cortical fractures in horses, but the delay in onset of bone formation may negate benefits. The hPTH(1-34) GAM used in this study should not be placed in articular subchondral bone defects, but contact with articular surfaces is unlikely to cause short-term adverse effects.

Strontium ranelate: a novel mode of action leading to renewed bone quality

Various bone resorption inhibitors and bone stimulators have been shown to decrease the risk of osteoporotic fractures. However, there is still a need for agents promoting bone formation by inducing positive uncoupling between bone formation and bone resorption. In vitro studies have suggested that strontium ranelate enhances osteoblast cell replication and activity. Simultaneously, strontium ranelate dose-dependently inhibits osteoclast activity. In vivo studies indicate that strontium ranelate stimulates bone formation and inhibits bone resorption and prevents bone loss and/or promotes bone gain. This positive uncoupling between bone formation and bone resorption results in bone gain and improvement in bone geometry and microarchitecture, without affecting the intrinsic bone tissue quality. Thus, all the determinants of bone strength are positively influenced. In conclusion, strontium ranelate, a new treatment of postmenopausal osteoporosis, acts through an innovative mode of action, both stimulating bone formation and inhibiting bone resorption, resulting in the rebalancing of bone turnover in favor of bone formation. Strontium ranelate increases bone mass while preserving the bone mineralization process, resulting in improvement in bone strength and bone quality.

Periosteum: biology, regulation, and response to osteoporosis therapies

Periosteum contains osteogenic cells that regulate the outer shape of bone and work in coordination with inner cortical endosteum to regulate cortical thickness and the size and position of a bone in space. Induction of periosteal expansion, especially at sites such as the lumbar spine and femoral neck, reduces fracture risk by modifying bone dimensions to increase bone strength. The cell and molecular mechanisms that selectively and specifically activate periosteal expansion, as well as the mechanisms by which osteoporosis drugs regulate periosteum, remain poorly understood. We speculate that an alternate strategy to protect human bones from fracture may be through targeting of the periosteum, either using current or novel agents. In this review, we highlight current concepts of periosteal cell biology, including their apparent differences from endosteal osteogenic cells, discuss the limited data regarding how the periosteal surface is regulated by currently approved osteoporosis drugs, and suggest one potential means through which targeting periosteum may be achieved. Improving our understanding of mechanisms controlling periosteal expansion will likely provide insights necessary to enhance current and develop novel interventions to further reduce the risk of osteoporotic fractures.

Intermittent Parathyroid Hormone Treatment Enhances Guided Bone Regeneration in Rat Calvarial Bone Defects

This study investigates the effects of intermittent parathyroid hormone (PTH(1-34)) treatment on bone regeneration and mechanical strength of critically sized rat calvarial bone defects covered with expanded membranes. A full-thickness bone defect (diameter 5 mm) was trephined in the central part of the parietal bones in 20-month-old female Wistar rats. The bone defects were covered with an exocranial and an endocranial expanded polytetrafluoroethylene membrane. The animals were killed 35 days after operation. 60 microg PTH(1-34)/kg was administered daily during the healing period, and control animals with calvarial bone defects were given vehicle. Mechanical testing was performed by a punch out testing procedure by placing a steel punch (diameter 3.5 mm) in the center of the healed defect. After mechanical testing, the newly formed tissue inside the defect was removed and the dry weight and ash weight were measured. PTH(1-34) increased dry weight by 48%, ash weight by 51%, and ash concentration by 26%. PTH(1-34) also augmented the mechanical strength of the new bone formed inside the defect by increasing ultimate stiffness by 87%. No differences in body weight were found between the vehicle-injected and the PTH-treated animals during the experiment. The experiment demonstrates that intermittent PTH(1-34) treatment increases bone deposition and enhances mechanical strength of healing rat calvarial defects covered with expanded polytetrafluoroethylene membranes.

Effects of hypophysectomy and recombinant human growth hormone on material and geometric properties and the pre- and post-yield behavior of femurs in young rats

To study the musculoskeletal effects of hypophysectomy (Hx) and a partial replacement treatment with recombinant human growth hormone (rhGH) in rats, we determined the stiffness (elastic modulus, E) and volumetric BMD (vBMD) of cortical bone; the periosteal and endosteal perimeters, area and bending moment of inertia (xCSMI) of the cross sections, and the structural stiffness and pre- and post-yield strength of the femur diaphyses by pQCT and mechanical tests, and the gastrocnemius weight of rats that were either intact (n = 9) or Hx at 15 days of age (20). The latter were otherwise untreated (Hx controls, 4) or given 0.4 (8) or 2.0 (8) IU kg(-1) day(-1), s.c., of rhGH for 45 days starting 15 days after surgery. Hx delayed musculoskeletal development (gastrocnemius weight, bone geometric properties), thus affecting the diaphyseal stiffness and strength. It also reduced the cortical vBMD through an undefined mechanism, and increased the elastic modulus of cortical bone. The Hx also affected the correlation between bone geometric and material properties (xCSMI vs. E), suggesting an antianabolic interaction with the biomechanical control of bone modeling in response to strains caused by mechanical usage. As a result, Hx reduced the stiffness, post-yield, and ultimate strength of the diaphyses. These effects should reflect changes in bone tissue microstructure, perhaps associated with crack generation and progress, but unrelated to bone mineral mass. They are compatible with the induction of a delay in collagen turnover with associated increases in fibers' diameter and crystals' size that may have resulted from the suppression of some other hormones, such as thyroid, prolactin, or other hormones regulated by ACTH. The above doses of rhGH significantly but incompletely prevented the negative Hx effects on bone and muscle development (bone geometric properties, muscle mass). However, rhGH treatment failed to prevent the demineralizing and stiffening effect of Hx on bone tissue and the unusual effects on the post-yield strength (less clearly related to muscle development than the former). Consequently, rhGH treatment tended to preserve the natural relationship between muscle function and bone geometry but not bone strength. The effects of larger rhGH doses and the interaction of other hormones with the described effects remain to be investigated. Nevertheless, these findings would deserve special attention because they challenge the prevailing view that in endocrine-metabolic bone-weakening diseases the bone matrix always has a normal composition.

Bone growth stimulators. New tools for treating bone loss and mending fractures

In the new millennium, humans will be traveling to Mars and eventually beyond with skeletons that respond to microgravity by self-destructing. Meanwhile in Earth's aging populations growing numbers of men and many more women are suffering from crippling bone loss. During the first decade after menopause all women suffer an accelerating loss of bone, which in some of them is severe enough to result in "spontaneous" crushing of vertebrae and fracturing of hips by ordinary body movements. This is osteoporosis, which all too often requires prolonged and expensive care, the physical and mental stress of which may even kill the patient. Osteoporosis in postmenopausal women is caused by the loss of estrogen. The slower development of osteoporosis in aging men is also due at least in part to a loss of the estrogen made in ever smaller amounts in bone cells from the declining level of circulating testosterone and is needed for bone maintenance as it is in women. The loss of estrogen increases the generation, longevity, and activity of bone-resorbing osteoclasts. The destructive osteoclast surge can be blocked by estrogens and selective estrogen receptor modulators (SERMs) as well as antiosteoclast agents such as bisphosphonates and calcitonin. But these agents stimulate only a limited amount of bone growth as the unaffected osteoblasts fill in the holes that were dug by the now suppressed osteoclasts. They do not stimulate osteoblasts to make bone--they are antiresorptives not bone anabolic agents. (However, certain estrogen analogs and bisphosphates may stimulate bone growth to some extent by lengthening osteoblast working lives.) To grow new bone and restore bone strength lost in space and on Earth we must know what controls bone growth and destruction. Here we discuss the newest bone controllers and how they might operate. These include leptin from adipocytes and osteoblasts and the statins that are widely used to reduce blood cholesterol and cardiovascular damage. But the main focus of this article is necessarily the currently most promising of the anabolic agents, the potent parathyroid hormone (PTH) and certain of its 31- to 38-aminoacid fragments, which are either in or about to be in clinical trial or in the case of Lilly's Forteo [hPTH-(1-34)] tentatively approved by the Food and Drug Administration for treating osteoporosis and mending fractures.

Effects of liver-derived insulin-like growth factor I on bone metabolism in mice

Insulin-like growth factor (IGF) I is an important regulator of both skeletal growth and adult bone metabolism. To better understand the relative importance of systemic IGF-I versus locally expressed IGF-I we have developed a transgenic mouse model with inducible specific IGF-I gene inactivation in the liver (LI-IGF-I-/-). These mice are growing normally up to 12 weeks of age but have a disturbed carbohydrate and lipid metabolism. In this study, the long-term effects of liver-specific IGF-I inactivation on skeletal growth and adult bone metabolism were investigated. The adult (week 8-55) axial skeletal growth was decreased by 24% in the LI-IGF-I-/- mice whereas no major reduction of the adult appendicular skeletal growth was seen. The cortical cross-sectional bone area, as measured in the middiaphyseal region of the long bones, was decreased in old LI-IGF-I-/- mice. This reduction in the amount of cortical bone was caused mainly by decreased periosteal circumference and was associated with a weaker bone determined by a decrease in ultimate load. In contrast, the amount of trabecular bone was not decreased in the LI-IGF-I-/- mice. DNA microarray analysis of 30-week-old LI-IGF-I-/- and control mice indicated that only four genes were regulated in bone whereas approximately 40 genes were regulated in the liver, supporting the hypothesis that liver-derived IGF-I is of minor importance for adult bone metabolism. In summary, liver-derived IGF-I exerts a small but significant effect on cortical periosteal bone growth and on adult axial skeletal growth while it is not required for the maintenance of the trabecular bone in adult mice.

Parathyroid hormone in the treatment of osteoporosis

Parathyroid hormone (PTH), especially intact human PTH [hPTH(1-84)] and its various fragments [hPTH(1-31), (1-34), (1-36), (1-38) and their modifications], has been used for the treatment of osteoporosis over the last 10 years. Although chronic continuous excess of PTH markedly increases bone resorption, as seen in the typical example of primary hyperparathyroidism and osteitis fibrosa generalisata, intermittent PTH administration has been found to stimulate bone formation in animals, providing a basis for the use of PTH as a therapeutic agent for osteoporosis. In addition to dramatically increasing trabecular bone density and also sustaining cortical bone density, PTH administration increases bone strength and reduces the fracture rate, despite occasional increases in cortical porosity. Administration of PTH in combination with antiresorptive agents such as estrogen, calcitonin, vitamin D and bisphosphonates augments its effect. Because of its bone anabolic action, PTH is expected to be effective for osteoporosis in those of advanced age with suppressed bone remodelling, which might not respond favourably to antiresorptive agents.

Preservation of bone mass in pediatric dialysis and transplant patients

Renal osteodystrophy continues to be a major challenge to the physician treating the child with end-stage renal disease (ESRD). The gold standard for the assessment of bone status is bone histomorphometry, which divides bone pathology into 3 main types; high-turnover, low-turnover, and mixed disease. The high-turnover disease, related to hyperparathyroidism, has been the one most extensively investigated; however, optimal therapy, especially in the growing child, is yet unclear. Overzealous treatment might result in adynamic bone disease (an extreme example of low-turnover disease), and further interference with statural growth. Pre-existent bone disease after kidney transplantation seems to worsen immediately, probably because of the high dose of corticosteroids used. In children who attain normal kidney function in the allograft, bone status seems to improve over time. Little is known about bone in transplanted patients with reduced glomerular filtration rate (GFR). The correlation between bone histology and its main surrogates, bone remodeling markers and bone mineral density, is yet unclear, but it might serve to follow the progress of an individual patient. New therapeutic modalities aimed at suppressing hyperparathyroidism, and consequently bone resorption, as well as agents directly attenuating bone resorption, should be further investigated for their effect on bone in patients with ESRD or after transplantation. Similarly, agents stimulating bone formation, particularly growth hormone, require further attention for their potential to improve bone status. Bone health and the child's somatic growth at ESRD or after kidney transplantation are closely related, and therapy should be aimed at achieving optimal results for both.

Increases in callus formation and mechanical strength of healing fractures in old rats treated with parathyroid hormone

We studied the effects of intermittent administration of parathyroid hormone (PTH(1-34)) on callus formation and mechanical strength of tibial fractures in 27-month-old rats after 3 and 8 weeks of healing. 200 microg PTH(1-34)/kg was administered daily during both periods of healing, and control animals with fractures were given vehicle. At 3 weeks, PTH treatment increased maximum load and external callus volume by 160% and 208%; at 8 weeks, by 270% and 135%. It also enhanced callus bone mineral content (BMC) by 190% and 388% (3 and 8 weeks). From week 3 to week 8, callus BMC increased by 60% in the vehicle-injected animals, and by 169% in the PTH-treated animals. In the contralateral intact tibia, PTH treatment increased BMC by 18% and 21% (3 and 8 weeks). No differences in body weight were found between the vehicle-injected and the PTH-treated animals during the experiment. In conclusion, PTH treatment enhances fracture strength, callus volume and callus BMC after 3 and 8 weeks of healing.

Experimental gerontology in the Nordic countries

Research in geriatric medicine developed in the Nordic countries in the 1950s, following the tradition from the United Kingdom. Quite early, longitudinal epidemiological studies of 'normal' ageing emerged. Now there are chairs in geriatric medicine at many of the medical schools. Experimental gerontology came much later, typically scattered in a variety of medical school departments. There is only one chair in gerontology (in Tampere). Two major research undertakings have emerged in recent years, the Danish Centre for Molecular Gerontology, and a cluster of research groups at the Division of Geriatrics at the Karolinska Institutet. Other research groups are found in Denmark at the universities in Aarhus, Copenhagen and Odense; in Finland at the universities in Jyväskylä, Kuopio, Tampere and Turku; and in Norway at the university in Trondheim. These activities are reviewed country-wise.