Skeletal response to corticosteroid deficiency and excess in growing male rats

Positive programming of the GC-IGF1 axis mediates adult osteoporosis susceptibility in male offspring rats induced by prenatal dexamethasone exposure

Prenatal dexamethasone exposure (PDE) can lead to offspring long bone dysplasia and continue to postnatal, and this is an important cause of fetal-derived osteoporosis. Studies have confirmed that intrauterine endogenous GC overexposure mediates multiple organ dysplasia and adult-related disease susceptibility in offspring through the glucocorticoid-insulin-like growth factor1 (GC-IGF1) axis. However, it remains unknown if exogenous dexamethasone can regulate bone development in offspring through the GC-IGF1 axis. We determined that the PDE fetal rats exhibited poor osteogenic differentiation, decreased bone mass that continued to adolescence, and increased susceptibility to osteoporosis in adulthood. Concurrently, PDE decreased the serum corticosterone concentration and IGF1 expression in offspring before and after birth, while the increased serum corticosterone concentration induced by chronic stress reversed the inhibition of IGF1 expression induced by PDE. Furthermore, PDE decreased the expression of GRα and miR-130a-5p, increased HDAC4, and decreased H3K27 acetylation in the IGF1 promoter region in bone tissue, and the above changes were negatively compensated after chronic stress. In vitro, a low concentration of corticosterone inhibited the expression of GRα and miR130a-5p, upregulated the expression of HDAC4, inhibited the promoter region H3K27 acetylation, and expression of IGF1 in bone marrow mesenchymal stem cell (BMSCs) osteoblast differentiated cells and inhibited osteogenic differentiation of BMSCs. GRα overexpression, miR-130a-5p mimic treatment, or HDAC4 siRNA exposure reversed the downstream molecular alterations caused by low corticosterone concentrations. In conclusion, PDE-induced intrauterine hypoglucocorticoid exposure could positively program IGF1 expression in bone tissue through the GRα/miR-130a-5p/HDAC4 pathways, thus mediating osteogenic dysdifferentiation and adult osteoporosis susceptibility in male offspring rats.

Bone Structural, Biomechanical and Histomorphometric Characteristics of the Hindlimb Skeleton in the Marsh Rice Rat (Oryzomys palustris)

INTRODUCTION

The rice rat (Oryzomys palustris) is a non-conventional laboratory rodent species used to model some human bone disorders. However, no studies have been conducted to characterize the postcranial skeleton. Therefore, we aimed to investigate age- and gender-related features of the hindlimb skeleton of this species.

METHODS

We used femurs and tibiae from 94 rats of both genders aged 4-28 wks. Bone mineral content (BMC), volumetric bone mineral density (vBMD), and biomechanical properties were determined in femurs. In addition, bone histomorphometry of tibiae was conducted to assess bone cell activities and bone turnover over time.

RESULTS

Bone length, total metaphysis BMC and vBMD, mid-diaphyseal BMC and vBMD, cortical thickness, and cortical area progressively augmented with age. Whereas the increase in these parameters plateaued at age 16-22 wks in female rats, they continued to rise to age 28 wks in male rats. Furthermore, bone strength parameters increased with age, with few differences between genders. We also observed a rapid decrease in longitudinal growth between ages 4-16 wks. Whereas young rats had a greater bone formation rate and bone turnover, older rice rats had greater bone volume and trabecular thickness, with no differences between genders.

CONCLUSIONS

1) Sexual dimorphism in the rice rat becomes grossly evident at age 16 wks; 2) the age-related increases in bone mass, structural cortical parameters, and in some biomechanical property parameters plateau at an older age in male than in female rats; and 3) bone growth and remodeling significantly decreased with age irrespective of the gender.

Bone health in glucocorticoid-treated childhood acute lymphoblastic leukemia

Glucocorticoids (GCs) are widely used in the treatment of childhood acute lymphoblastic leukemia (ALL), but their long-term use is also associated with bone-related morbidities. Among others, growth deficit, decreased bone mineral density (BMD) and increased fracture rate are well-documented and severely impact quality of life. Unfortunately, no efficient treatment for the management of bone health impairment in patients and survivors is currently available. The overall goal of this review is to discuss the existing data on how GCs impair bone health in pediatric ALL and attempts made to minimize these side effects.

Gene Expression and Resistance to Glucocorticoid-Induced Apoptosis in Acute Lymphoblastic Leukemia: A Brief Review and Update

BACKGROUND

Resistance to glucocorticoid (GC)-induced apoptosis in Acute Lymphoblastic Leukemia (ALL), is considered one of the major prognostic factors for the disease. Prednisolone is a corticosteroid and one of the most important agents in the treatment of acute lymphoblastic leukemia. The mechanics of GC resistance are largely unknown and intense ongoing research focuses on this topic.

AIM

The aim of the present study is to review some aspects of GC resistance in ALL, and in particular of Prednisolone, with emphasis on previous and present knowledge on gene expression and signaling pathways playing a role in the phenomenon.

METHODS

An electronic literature search was conducted by the authors from 1994 to June 2019. Original articles and systematic reviews selected, and the titles and abstracts of papers screened to determine whether they met the eligibility criteria, and full texts of the selected articles were retrieved.

RESULTS

Identification of gene targets responsible for glucocorticoid resistance may allow discovery of drugs, which in combination with glucocorticoids may increase the effectiveness of anti-leukemia therapies. The inherent plasticity of clinically evolving cancer justifies approaches to characterize and prevent undesirable activation of early oncogenic pathways.

CONCLUSION

Study of the pattern of intracellular signal pathway activation by anticancer drugs can lead to development of efficient treatment strategies by reducing detrimental secondary effects.

Bone phenotype in melanocortin 2 receptor-deficient mice

Considering that stress condition associated with osteoporosis, the hypothalamic-pituitary-adrenal (HPA) axis, which is essential for central stress response system, is implicated in regulating bone mass accrual. Melanocortin 2 receptor (MC2R), the receptor of adrenocorticotropic hormone is expressed in both adrenal gland cells and bone cells. To elucidate the role of HPA axis in bone metabolism, we assessed the skeletal phenotype of MC2R deficient mice (MC2R ^-/- mice). We first examined bone mineral density and cortical thickness of femur using dual x-ray absorptiometry and micro-computed tomography. We then conducted histomorphometric analysis to calculate the static and dynamic parameters of vertebrae in MC2R ^-/- mice. The levels of osteoblastic marker genes were examined by quantitative PCR in primary osteoblasts derived from MC2R ^-/- mice. Based on these observations, bone mineral density of femur in MC2R ^-/- mice was increasing relative to litter controls. Meanwhile, the thickness of cortical bone of femur in MC2R ^-/- mice was remarkably elevated. Moreover, serum osteocalcin level was drastically raised in MC2R ^-/- mice. However, bone histomorphometry revealed that static and dynamic parameters reflecting bone formation and resorption were unchanged in vertebrae of MC2R ^-/- mice compared to the control, indicating that MC2R function may be specific to appendicular bone than axis bone. Taken together, the HPA axis due to deletion of MC2R is involved in bone metabolism.

Effect of Leptin Deficiency on the Skeletal Response to Hindlimb Unloading in Adult Male Mice

Based on body weight, morbidly obese leptin-deficient ob/ob mice have less bone than expected, suggesting that leptin plays a role in the skeletal response to weight bearing. To evaluate this possibility, we compared the skeletal response of wild type (WT) and ob/ob mice to hindlimb unloading (HU). Mice were individually housed at 32 °C (thermoneutral) from 4 weeks of age (rapidly growing) to 16 weeks of age (approaching skeletal maturity). Mice were then randomized into one of 4 groups (n = 10/group): (1) WT control, (2) WT HU, (3) ob/ob control, and (4) ob/ob HU and the results analyzed by 2-way ANOVA. ob/ob mice pair-fed to WT mice had normal cancellous bone volume fraction (BV/TV) in distal femur, lower femur length and total bone area, mineral content (BMC) and density (BMD), and higher cancellous bone volume fraction in lumbar vertebra (LV). HU resulted in lower BMC and BMD in total femur, and lower BV/TV in distal femur and LV in both genotypes. Cancellous bone loss in femur in both genotypes was associated with increases in osteoclast-lined bone perimeter. In summary, leptin deficiency did not attenuate HU-induced osteopenia in male mice, suggesting that leptin is not required for bone loss induced by unweighting.

Supraphysiologic glucocorticoid administration increased biomechanical bone strength of rats' vertebral body

The aim of this study is to assess the effects of different glucocorticoid administration protocols on biomechanical properties of the first lumbar vertebral body in rats. We divided 40 male rats into the following groups: control, dexamethasone (7 mg/week), dexamethasone (0.7 mg/week), methylprednisolone (7 mg/kg/week), methylprednisolone (5 mg/kg twice weekly), dexamethasone (7 mg/kg three times per week), dexamethasone (0.7 mg/kg three times per week, and low-level laser treated rats. Lumbar vertebrae in rats were exposed to the pulsed laser. We conducted a biomechanical test to examine the mechanical properties of vertebral body in rats' lumbar bone. Supraphysiologic glucocorticoid administration protocols did not impair the biomechanical properties of rats' vertebral bodies compared to control and laser-treated rats. Supraphysiologic glucocorticoid administration caused an anabolic effect on the vertebral bodies.

Evaluating glucocorticoid administration on biomechanical properties of rats' tibial diaphysis

BACKGROUND

Osteoporosis is a disease, which causes bone loss and fractures. Although glucocorticoids effectively suppress inflammation, their chronic use is accompanied by bone loss with a tendency toward secondary osteoporosis.

OBJECTIVES

This study took into consideration the importance of cortical bone in the entire bone's mechanical competence. Hence, the aim of this study was to assess the effects of different protocols of glucocorticoid administration on the biomechanical properties of tibial bone diaphysis in rats compared to control and low-level laser-treated rats.

MATERIALS AND METHODS

This experimental study was conducted at Shahid Beheshti University of Medical Sciences, Tehran, Iran. We used systematic random sampling to divide 40 adult male rats into 8 groups with 5 rats in each group. Groups were as follows: 1) control, 2) dexamethasone (7 mg/week), 3) dexamethasone (0.7 mg/week), 4) methylprednisolone (7 mg/kg/week), 5) methylprednisolone (5 mg/kg twice weekly), 6) dexamethasone (7 mg/kg three times per week), 7) dexamethasone (0.7 mg/kg thrice per week), and 8) low-level laser-treated rats. The study periods were 4-7 weeks. At the end of the treatment periods, we examined the mechanical properties of tibial bone diaphysis. Data were analyzed by statistical analyses.

RESULTS

Glucocorticoid-treated rats showed weight loss and considerable mortality (21%). The biomechanical properties (maximum force) of glucocorticoid-treated rats in groups 4 (62 ± 2.9), 6 (63 ± 5.1), and 7 (60 ± 5.3) were comparable with the control (46 ± 1.5) and low-level laser-treated (57 ± 3.2) rats.

CONCLUSIONS

In contrast to the findings in humans and certain other species, glucocorticoid administration caused anabolic effect on the cortical bone of tibia diaphysis bone in rats.

Animal models for osteoporosis

The major types of osteoporosis in humans are postmenopausal osteoporosis, disuse osteoporosis, and glucocorticoid-induced osteoporosis. Animal models for postmenopausal osteoporosis are generated by ovariectomy. Bone loss occurs in estrogen deficiency due to enhanced bone resorption and impaired osteoblast function. Estrogen receptor α induces osteoclast apoptosis, but the mechanism for impaired osteoblast function remains to be clarified. Animal models for unloading are generated by tail suspension or hind limb immobilization by sciatic neurectomy, tenotomy, or using plaster cast. Unloading inhibits bone formation and enhances bone resorption, and the involvement of the sympathetic nervous system in it needs to be further investigated. The osteocyte network regulates bone mass by responding to mechanical stress. Osteoblast-specific BCL2 transgenic mice, in which the osteocyte network is completely disrupted, can be a mouse model for the evaluation of osteocyte functions. Glucocorticoid treatment inhibits bone formation and enhances bone resorption, and markedly reduces cancellous bone in humans and large animals, but not consistently in rodents.

Free vascularized fibular grafting for patients receiving postoperative corticosteroids

Free vascularized fibular grafting (FVFG) is an effective method to treat corticosteroid-induced osteonecrosis of the femoral head (ONFH). Some patients continued to receive maintenance doses of corticosteroids to treat the primary disease postoperatively. This study was performed to evaluate outcomes of FVFG for corticosteroid-induced ONFH in patients who continued to receive corticosteroids postoperatively. The authors retrospectively reviewed the records of 44 patients (78 hips) who had received corticosteroid treatment for their primary disease after FVFG. They were followed up for at least 2 years (mean, 5.6 years). Demographic details, Harris Hip scores, the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36), and radiographic data were collected and analyzed. The mean Harris Hip score for all hips was 70.9±9.9 points before surgery and increased to 84±12.1 points at the latest follow-up. There were also significant increases (P<.05) in physical component summary score and mental component summary score. According to the latest radiographic evaluation, 49 hips (62.8%) appeared improved, 10 hips (12.8%) appeared unchanged, and only 19 hips (24.4%) appeared worse. Seven hips (9%) underwent total hip arthroplasty during the follow-up period. Therefore, the results showed that FVFG was a viable method of treating corticosteroid-induced ONFH in patients who receive maintenance doses of corticosteroids postoperatively.

The effect of postoperative corticosteroid administration on free vascularized fibular grafting for treating osteonecrosis of the femoral head

Free vascularized fibular grafting (FVFG) has been reported to be an effective method of treating osteonecrosis of the femoral head (ONFH). This study evaluated whether postoperative maintenance doses of corticosteroids had an adverse effect on FVFG outcomes in patients with corticosteroid-induced ONFH. We retrospectively reviewed the records of 39 patients (67 hips) who had received maintenance doses of corticosteroids following FVFG. This group was matched to a group of patients who had not received corticosteroids treatment after operation. The mean follow-up duration was 5.4 years for the postoperative corticosteroid administration group (PCA group) and 5.0 years for the control group. At the latest follow-up, the average increase in Harris hip score was 11.1 ± 8.7 points for all hips in the PCA group and 12.6 ± 7.4 points for all hips in the control group (P > 0.05). In the PCA group, through radiographic evaluation, 49 hips were improved, 10 hips appeared unchanged, and 8 hips appeared worse. In the control group, 47 hips were improved, 13 hips appeared unchanged, and 7 hips appeared worse. The results suggested that postoperative maintenance doses of corticosteroids do not have an adverse effect on FVFG outcomes in patients with corticosteroid-induced ONFH.

Mechanical vibration preserves bone structure in rats treated with glucocorticoids

Glucocorticoids are an important cause of secondary osteoporosis in humans, which decreases bone quality and leads to fractures. Mechanical stimulation in the form of low-intensity and high-frequency vibration seems to be able to prevent bone loss and to stimulate bone formation. The objective of this study was to evaluate the effects of mechanical vibration on bone structure in rats treated with glucocorticoids. Thirty 3-month-old adult male Wistar rats were randomized to three groups: control (C), glucocorticoid (G), and glucocorticoid with vibration (GV). The G and GV groups received 3.5mg/kg/day of methylprednisolone 5 days/week for a duration of 9 weeks, and the C group received vehicle (saline solution) during the same period. The GV group was vibrated on a special platform for 30 min per day, 5 days per week during the experiment. The platform was set to provide a vertical acceleration of 1 G and a frequency of 60 Hz. Skeletal bone mass was evaluated by total body densitometry (DXA). Fracture load threshold, undecalcified bone histomorphometry, and bone volume were measured in tibias. Glucocorticoids induced a significantly lower weight gain (-9.7%) and reduced the bone mineral content (-9.2%) and trabecular number (-41.8%) and increased the trabecular spacing (+98.0%) in the G group, when compared to the control (C). Vibration (GV) was able to significantly preserve (29.2%) of the trabecular number and decrease the trabecular spacing (+26.6%) compared to the G group, although these parameters did not reach C group values. The fracture load threshold was not different between groups, but vibration significantly augmented the bone volume of the tibia by 21.4% in the GV group compared to the C group. Our study demonstrated that low-intensity and high-frequency mechanical vibration was able to partially inhibit the deleterious consequences of glucocorticoids on bone structure in rats.

Glucocorticoid inhibits bone regeneration after osteonecrosis of the femoral head in aged female rats

Idiopathic osteonecrosis of the femoral head (ION) is a painful disease of the hip, the pathogenic mechanism of which is still unclear. The most common extraneous factor is steroid treatment. Steroids have inhibiting effects on bone formation and resorption. When bone regenerative treatments are indicated for ION patients who are exposed to steroids, we cannot ignore the effects of corticosteroid itself on bone healing. The aim of this study was to investigate the effects of glucocorticoid on bone regeneration after osteonecrosis of the femoral head in a rat model. Osteonecrosis was induced surgically on the left femoral heads of aged female rats (about 6 months old) on day 0. Methylprednisolone sodium succinate (MPSS) or normal saline was administrated at a dose of 100 mg/kg/day from day 7 to 11. Femoral heads were analyzed histologically. There were no pathological findings in the right femoral heads of the MPSS-treated and saline-treated rats, as control for the contralateral injury. The newly formed bone volume and the osteoclast number were significantly smaller in the MPSS-treated group. The normal bone marrow was regenerated in the saline-treated group, whereas most of the bone marrow space still contained fibroblast-like spindle-shaped cells in the MPSS-treated group on day 42. Alkaline phosphatase-positive cells were only seen in the areas around the regenerated bone marrow cavities. Thus, MPSS inhibits bone formation by suppressing osteoblast proliferation and resorption by suppressing the recruitment of osteoclast precursors. These findings may be useful when designing treatments for ION patients exposed to steroids.

Effects of the administration of corticosterone, parathyroid hormone, or both, and of their withdrawal, on rat bone and cartilage histomorphometric parameters, and on osteoprotegerin and RANKL mRNA expression and proteins

We have studied the effects of the treatment with corticosterone (CORT), parathyroid hormone (PTH), or both (CORT + PTH), and of their withdrawal (CORT-rec and CORT + PTH-rec), on the osteoprotegerin (OPG) and receptor activator of nuclear factor-kB ligand (RANKL) localization and expression and on histomorphometric parameters in primary and secondary spongiosa of rat femur and tibia metaphyses. In the secondary spongiosa of the CORT group, the bone remodeling and the OPG/RANKL mRNA ratio decreased. In the PTH group, the bone turnover and the structural and connectivity indices increased, and the OPG/RANKL mRNA ratio fell; this ratio rose, however, in the primary spongiosa. In the CORT + PTH group, remodeling values intermediate between those of the CORT and PTH groups, were detected in the secondary spongiosa, where OPG and RANKL mRNA rose. Return towards control values was found in the recovery groups. The Cartilage Growth Plate Width was reduced in the CORT and CORT + PTH groups and returned to normal values in the recovery groups, while it was not affected by PTH. Independently of treatments, both OPG and RANKL mRNA and proteins were co-localized in the same cartilage and bone cells and in several bone marrow cells. In conclusion, the catabolic effects induced by CORT treatment occur together with an OPG fall and a RANKL rise. In the PTH group in which the bone turnover increase, the OPG and RANKL mRNA expressions differ in the primary and secondary spongiosa, confirming that the bone tissue in these sites can have different metabolic trends.

High dose glucocorticoid hampers bone formation and resorption after bone marrow ablation in rat

We analyzed the effect of glucocorticoid on bone regeneration after bone marrow ablation in tibiae of 8-week-old rats. Methylprednisolone sodium succinate (MPSS) was injected intramuscularly at a dose of 100 mg/kg/day for 3 days. Tibiae on days 1, 3, 5, 7, 10, 12, and 14 after ablation were subjected to tartrate-resistant acid phosphatase staining, immunohistochemistry, in situ hybridization, and transmission electron microscopy (TEM), and measurement of the volume of newly-formed bone and the osteoclast number. MPSS significantly decreased the newly-formed bone volume on day 7, and immature bone still remained on day 10 in the MPSS-treated group. The volume of this bone was significantly higher than that in the control group. However, there were no differences between the groups in the osteoclast number, the expression of mRNAs for osteoblast differentiation markers, and alkaline phosphatase and cathepsin K judged by immunohistochemistry. TEM findings showed no difference in the form of osteoblasts, whereas osteoclasts in the MPSS-treated group had less developed ruffled borders, compared to those in the control group. These results suggest that MPSS treatment affects neither the differentiation nor the shape of osteoblasts, and does not change the osteoclast number or the cathepsin K level. However, high dose MPSS inhibits both bone formation and resorption during bone regeneration after rat tibial bone marrow ablation, and inhibits ruffled border formation in osteoclasts. These data will be useful to develop bone regenerative therapies for bone diseases due to high dose steroid administration.

Recommendations for the Registration of Agents to be Used in the Prevention and Treatment of Glucocorticoid-Induced Osteoporosis: Updated Recommendations from the Group for the Respect of Ethics and Excellence in Science

OBJECTIVES

The Group for the Respect and Excellence in Science (GREES) has reviewed and updated their recommendations for clinical trials to evaluate the efficacy and safety of new chemical entities to be used in the treatment and prevention of glucocorticoid-induced osteoporosis (GIOP).

METHODS

Consensus discussion of the committee.

RESULTS

With the exception of steroid use posttransplantation, there is no need to differentiate between underlying diseases. Prevention and treatment for GIOP are dependent on exposure to glucocorticoids rather than T-scores as in postmenopausal osteoporosis (PMO). If fracture data are obtained for PMO, it need not be repeated for GIOP, relying instead on bone mineral density (BMD) trials of at least 1 year. GREES recommends several changes in the previous guidance for GIOP. The committee saw no need to repeat preclinical studies if those have been previously done to assure bone quality in PMO. Similarly, phase I and phase II trials, if careful dose selection has been done for PMO, should not be repeated. The "prevention" and "treatment" claims should remain. Since the most recent evidence suggests significant increase in fracture risk for daily doses of prednisone of 5 mg/day or equivalent, clinical trials should concentrate on patients receiving at least this daily dosage. The emergence of bisphosphonates as the reference treatment, together with the rapid bone loss and high fracture incidence in glucocorticoid users, necessitates recommending a noninferiority trial design with lumbar spine BMD as the primary endpoint after 1 year.

CONCLUSIONS

Registration of new chemical entities to be used in the management of GIOP should be granted, based on a 1-year noninferiority trial, using BMD as primary outcome and alendronate or risedronate as comparator. Demonstration of antifracture efficacy should have been previously demonstrated in PMO.

The effect of purified compared with nonpurified diet on bone changes induced by hindlimb suspension of female rats

The purpose of this study was to compare the bone changes induced by unloading in rats fed different diets, because space flight studies use a semipurified diet, whereas space flight simulation studies typically use nonpurified diets. Female Sprague-Dawley rats were fed a purified American Institute of Nutrition (AIN) 93G diet or a standard nonpurified diet and kept ambulatory or subjected to unloading by hindlimb suspension (HLS) for 38 days. Bone mineral content (BMC), mechanical strength, and factors related to the diet that affect bone (i.e., urinary calcium excretion, estradiol, and corticosterone) were measured. Average food intakes (grams per day) differed for diets, but caloric intake (kilocalories per day) and the final body masses of treatment groups were similar. The HLS-induced decrease in femoral BMC was not statistically different for rats fed a nonpurified diet (-8.6%) compared with a purified AIN-93G diet (-11.4%). The HLS-induced decrease in femoral mechanical strength was not statistically different for rats fed a nonpurified diet (-24%) compared with a purified AIN-93G diet (-31%). However, bone lengths were decreased (P < 0.05) in rats fed a nonpurified diet compared with a purified diet. Plasma estradiol levels were lower (P < 0.05) in the HLS/AIN-93G group but similar in the HLS and ambulatory rats fed a nonpurified diet. Plasma estradiol was related to femoral BMC (r = 0.85, P < 0.01). Urinary calcium excretion was higher (P < 0.05) in rats fed a nonpurified diet than those fed a purified AIN-93G diet, which is consistent with the higher level of calcium in the nonpurified diet. Urinary corticosterone levels were higher (P < 0.05) in rats fed a nonpurified diet than rats fed the AIN-93G diet. Although the osteopenia induced by unloading was similar in both diet groups, there were differences in longitudinal bone growth, calcium excretion, plasma estradiol levels, and urinary corticosterone levels. Results indicate that the type of standard diet used is an important factor to consider when measuring bone end points.

Effects of disrupted β1-integrin function on the skeletal response to short-term hindlimb unloading in mice

The study was designed to determine whether β1-integrin plays a role in mediating the acute skeletal response to mechanical unloading. Transgenic (TG) mice were generated to express a dominant negative form of β1-integrin under the control of the osteocalcin promoter, which targets expression of the transgene to mature osteoblasts. At 63 days of age, wild-type (WT) and TG mice were subjected to hindlimb unloading by tail suspension for 1 wk. Pair-fed, normally loaded WT and TG mice served as age-matched controls. Bone samples from each mouse were processed for quantitative bone histomorphometry and biomechanical testing. The skeletal phenotype of TG mice was characterized by lower cancellous bone mass in the distal femoral metaphysis (−52%) and lumbar vertebral body (−20%), reduced curvature of the proximal tibia (−20%), and decreased bone strength (−20%) and stiffness (−23%) of the femoral diaphysis with relatively normal indexes of cancellous bone turnover. Hindlimb unloading for only 1 wk induced a 10% decline in tibial curvature and a 30% loss of cancellous bone in the distal femur due to a combination of increased bone resorption and decreased bone formation in both WT and TG mice. However, the strength and stiffness of the femoral diaphysis were unaffected by short-term hindlimb unloading in both genotypes. The observed increase in osteoclast surface was greater in unloaded TG mice (92%) than in unloaded WT mice (52%). Cancellous bone formation rate was decreased in unloaded WT (−29%) and TG (−15%) mice, but, in contrast to osteoclast surface, the genotype by loading interaction was not statistically significant. The results indicate that altered integrin function in mature osteoblasts may enhance the osteoclastic response to mechanical unloading but that it does not have a major effect on the development of cancellous osteopenia in mice during the early stages of hindlimb unloading.

Growth hormone can reverse glucocorticoid-induced low bone turnover on cortical but not on cancellous bone surfaces in adult Wistar rats

We evaluated the effect of glucocorticoids (GC) and growth hormone (GH) on cortical and cancellous bone turnover in adult rats using random vertical sections giving valid measurements of bone surfaces and bone formation parameters. GH administration could reverse GC-induced osteopenia and low bone turnover of cortical bone. However, GH could not reverse the GC-induced low bone turnover of cancellous bone.

METHODS

Seventy female Wistar rats, 7 months of age, were divided into five groups: (1) start control, (2) saline, (3) GC 9 mg/kg/day (Solu Medrol), (4) GH 5 mg/kg/day, and (5) GC 9 mg/kg/day + GH 5 mg/kg/day, and injected for 3 months. The vertebral body was examined using dynamic histomorphometry and biomechanical tests. Nonparametric methods were used.

RESULTS

Glucocorticoid administration induced a low bone turnover state of both the cortical and cancellous bone of the vertebral body, without altering the absolute amount of bone or the biomechanical competence of the vertebral body. GH administration induced a small increase in longitudinal bone growth and ventral modeling drift. This growth increased the total amount of cortical, endocortical, and cancellous bone in the vertebra. The biomechanical competence of a 3.5-mm-high cylinder of the central vertebral body was also increased due to an increase in the amount of cortical bone, whereas the total amount of cancellous bone in the cylinder was unaltered. The cancellous bone density (CBV) was, however, increased due to thicker trabeculae probably induced by an accelerated mineral appositional rate (MAR) induced by GH. GH also increased longitudinal and ventral modeling drifts in the GC-injected animals. GH increased the amount of cortical bone and also the amount of cancellous bone close to the epiphyseal growth plate, whereas the cancellous bone volume of the central vertebral cylinder was unaffected by GH administration in GC-injected animals. GH could also increase parameters of bone formation (bone mineralizing surface (MS) and MAR) on cortical bone surfaces in GC-injected animals, whereas parameters of bone formation [MS and bone formation rates (BFR)] on cancellous bone surfaces were even lower than those of animals injected with GC alone.

CONCLUSION

GH can reverse GC-induced low bone turnover on cortical but not on cancellous bone surfaces.

Absolute and relative growth of the rat craniofacial skeleton

Growth of the craniofacial region involves a mosaic of intramembranous and endochondral growth sites that grow at varying rates and mature at different times.

OBJECTIVE

The goal of this study was to compare absolute and relative growth of the craniofacial skeleton in wild-type Lewis rats to measures of somatic growth.

DESIGN

Lateral and dorsoventral X-rays of the head as well as the hindlimb were obtained weekly from 4 to 9 weeks of age. The X-rays were scanned, digitized, and selected linear distances were measured between points. Multilevel statistical models were used to generate absolute growth curves.

RESULTS

Although most growth curves were linear, several were quadratic (exhibiting a deceleration with age), and one displayed a third-order curve. Considerable variation in relative maturity was evident at the first time interval, ranging from 42% of mature (9 week) size (weight) to 97% of mature size (cranial width). Tibial length and body weight were less mature than most, but not all, craniofacial measures. With one exception (bizygomatic width), width measures were relatively more mature than vertical or depth measures. Vertical measures tended to be among the least mature of the craniofacial dimensions. Among the depth (length) measurements, there was a trend of higher maturity for cranial vault/cranial base measures and lower maturity for facial measures.

CONCLUSIONS

The wide spectrum of relative and absolute growth potentials demonstrated in this study indicate that the rodent craniofacial complex is amenable to testing the hypothesis that a component's response potential is related to its growth potential.

Histopathologic changes in metabolic bone disease

Metabolic bone disease encompasses a heterogeneous group of disorders that influence skeletal metabolism and structure. They are generally diagnosed at an advanced stage and manifest clinically with stunted skeletal growth in children and pathologic fractures in adults. Biochemical markers for bone metabolism are equivocal and microscopic examination of labeled bone remains the gold standard for the diagnosis and accurate monitoring of the response to therapy. This article reviews the role of microscopic bone changes in the diagnosis and management of metabolic bone disease.

Masculinized finger length patterns in human males and females with congenital adrenal hyperplasia

The ratio of the length of the second digit (2D) to the length of the fourth digit (4D) is greater in women than in men. Since androgens are involved in most somatic sex differences and since the sexual dimorphism in 2D:4D is stable from 2 years of age in humans, it was hypothesized that finger length pattern development might be affected by early androgen exposure. Human females with congenital adrenal hyperplasia (CAH) are exposed prenatally to higher than normal levels of adrenal androgens, providing an opportunity to test the effects of early androgen exposure on digit ratios. The 2D:4D was calculated for females with CAH, females without CAH, males with CAH, and males without CAH. Females with CAH had a significantly smaller 2D:4D on the right hand than did females without CAH. Males with CAH had a significantly smaller 2D:4D on the left hand than did males without CAH. A subset of six males with CAH had a significantly smaller 2D:4D on both hands compared with their male relatives without CAH. These results are consistent with the idea that prenatal androgen exposure reduces the 2D:4D and plays a role in the establishment of the sex difference in human finger length patterns. Finger lengths may therefore offer a retrospective marker of perinatal androgen exposure in humans.

Glucocorticoid-induced osteopenia in the mouse as assessed by histomorphometry, microcomputed tomography, and biochemical markers

Glucocorticoids are potent anti-inflammatory molecules used in the treatment of asthma, rheumatoid arthritis, inflammatory bowel disease, and other inflammatory and dermatological diseases, as well as in posttransplantation immunotherapy. Although glucocorticoids have been prescribed for many years, their potential side effects, when administered orally, can prevent their long-term use. The most serious side effect observed in the clinic is glucocorticoid-induced osteoporosis (GIOP). To develop a small animal model to characterize glucocorticoid-induced bone loss, we carried out a series of experiments using BALB/c mice given daily intraperitoneal doses of the synthetic glucocorticoid, dexamethasone. Following dexamethasone treatment, the mice became osteopenic, with highly significant decreases in bone formation rate and mineral apposition rate, as assessed by standard histomorphometry. Moreover, 3 week treatment with dexamethasone resulted in a decrease in trabecular thickness and trabecular number with an increase in surface-to-volume ratio of trabeculae in the distal femur, as measured using microcomputed tomography (micro-CT). The serum bone formation marker, osteocalcin, was dose-dependently decreased in all mice treated with dexamethasone and showed a parallel extent of regulation to the bone formation rate changes. In addition, serum levels of leptin, recently identified as playing a role in the regulation of bone mass, increased following dexamethasone treatment. BALB/c mice therefore represent a useful model system in which the detrimental effects of glucocorticoids on bone can be studied.

Genetics of osteoporosis: role of steroid hormone receptor gene polymorphisms

Osteoporosis is a common skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue with a consequent increase in bone fragility and susceptibility to fracture. In the past years, twin and family study have shown that this disease recognizes a strong genetic component and that genetic factors play an important role in regulating bone mineral density (BMD). While in few isolate conditions osteoporosis can be inherited in a simple Mendelian pattern, due to single gene mutations, in the majority of cases has to be considered a multifactorial polygenic disease in which genetic determinants are modulated by hormonal, environmental and nutritional factors. Given the important role that steroid hormones play in bone cell development and in the maintenance of normal bone architecture, polymorphisms at receptor of the steroid/thyroid hormone receptor superfamily, such as estrogen receptor alpha (ERalpha) and Vitamin D receptor (VDR) have been thoroughly investigated in the last years and appeared to represent important candidate genes. The individual contribution of these genetic polymorphisms to the pathogenesis of osteoporosis remains to be universally confirmed and an important aim in future work will be to define their functional molecular consequences and how these polymorphisms interact with each other and with the environment to cause the osteoporotic phenotype. A further promising application of genetic studies in osteoporosis comes from their pharmacogenomic implications, with the possibility to give a better guidance for therapeutic agents commonly used to treat this invalidating disorder or to identify target molecules for new therapeutic agents.

Recovery from osteoporosis through skeletal growth: early bone mass acquisition has little effect on adult bone density

It is often assumed that bone mineral accretion should be optimized throughout childhood to maximize peak bone mass. In contrast, we hypothesized that bone mineral acquisition early in life would have little or no effect on adult bone mass because many areas of the juvenile skeleton are replaced in toto through skeletal growth. To test this hypothesis, we induced osteoporosis by administering dexamethasone to 5-week-old rabbits for 5 weeks and then allowed them to recover for 16 weeks. Tibial bone mineral density (ash weight/volume) was decreased in the dexamethasone-treated animals at the end of treatment but recovered completely. Bone structure in the femur was assessed by histomorphometry. Trabecular and cortical bone in the distal metaphysis was made osteoporotic by dexamethasone, but was then replaced through endochondral bone formation and recovered. Periosteal bone formation rate in the diaphysis was decreased during dexamethasone treatment but afterwards rebounded above controls and normalized cortical width. Our data suggest that bone mineral acquisition early in life has little effect on adult bone density because the juvenile bone is largely replaced through growth. If this concept generalizes, then interventions to maximize peak bone mass should be directed at adolescents rather than young children.

Comparison of osteopenia after gastrectomy, ovariectomy and prednisolone treatment in the young female rat

Rat models of osteopenia include ovariectomy and long-term glucocorticoid treatment. Although ovariectomy produces significant trabecular bone loss after 2 weeks, long-term glucocorticoid treatment has been reported to cause osteopenia in some studies but not in others. In the present 8-week-study, we compared the osteopenia associated with gastrectomy (GX) to that induced by ovariectomy (OVX) or prednisolone (PRE) treatment. Female Sprague-Dawley rats (10 weeks old) were subjected to GX, OVX, PRE treatment or SHAM operation. At the end of the study, calvariae, femurs and fifth lumbar vertebrae (L5) were collected and subjected to bone density measurement (femur and L5), transillumination (calvaria) and histomorphometry (calvaria and femur). Bone density was reduced in L5 and the distal femur in the OVX and GX groups, but not in the PRE group. Transillumination of the calvaria showed marked bone loss in the GX rats, but not in the other groups. Morphometric analysis of the femur revealed reduced trabecular bone volume, trabecular thickness, trabecular number and osteoclast number, but increased osteoclast surface (expressed as per cent of the trabecular bone surface covered by osteoclasts) in the GX and OVX rats. The PRE rats seemed unaffected. Cortical thickness was reduced in the GX rats, but not in the other groups. The findings indicate that GX induces osteopenia in, e.g., femur and vertebra of a magnitude similar to or greater than that induced by OVX, while at the same time inducing osteopenia in the calvaria. Although osteoclast activation seems to contribute, the precise mechanism underlying the GX-evoked osteopenia remains obscure.

Immunosuppressant use without bone loss--implications for bone loss after transplantation

Cyclosporine A (CsA) is associated with posttransplantation bone disease. Immunosuppressant drugs such as sirolimus (SRL), which are more potent and less deleterious than CsA, are being developed. Previous experiments have shown that SRL although immunosuppressive, is relatively bone sparing. The use of low doses of CsA and SRL in combination has displayed in vivo synergism. This study was initiated to examine the effect of low-dose CsA and SRL on bone metabolism, thereby hopefully providing a bone sparing immunosuppressive regimen for transplant recipients. One hundred and nineteen rats were divided into groups: basal, vehicle, CsA high dose, CsA low dose, SRL low dose, and combination low-dose CsA and SRL. The basal group was killed on day 0 for histomorphometry. The experimental groups were weighed and bled on days 0, 28, 56, and 84 and were killed on day 84 for histomorphometry. Serial assays for blood urea nitrogen (BUN), creatinine, and osteocalcin were performed. Osteocalcin was raised on days 28 and 56 in the high dose CsA group. Histomorphometry showed osteopenia with high-dose CsA. Low-dose CsA was relatively bone sparing, while low-dose SRL and combined low-dose CsA did not cause bone loss. In conclusion, the synergistic combination of low-dose CsA and SRL has the potential of providing both bone sparing and immunosuppressive benefits.

Spaceflight inhibits bone formation independent of corticosteroid status in growing rats

Bone formation and structure have been shown repeatedly to be altered after spaceflight. However, it is not known whether these changes are related to a stress-related altered status of the corticosteroid axis. We investigated the role of corticosteroids on spaceflight-induced effects in rat pelvis and thoracic vertebrae. Thirty-six male Sprague-Dawley rats were assigned to a flight, flight control, or vivarium group (n = 12/group). Bilateral adrenalectomy was performed in six rats per group, the additional six rats undergoing sham surgery. Adrenalectomized (ADX) rats were implanted with corticosteroid pellets. On recovery from spaceflight, thoracic vertebrae and the whole pelvis were removed and processed for biochemistry, histomorphometry, or bone cell culture studies. The 17-day spaceflight resulted in decreased bone volume (BV) in the cotyle area of pelvic bones (-12%; p < 0.05) associated with approximately 50% inhibition of bone formation in the cancellous area of pelvic metaphyses and in thoracic vertebral bodies. The latter effect was associated with a decreased number of endosteal bone cells isolated from the bone surface (BS) in these samples (-42%; p < 0.05). This also was associated with a decreased number of alkaline phosphatase positive (ALP+) endosteal bone cells at 2 days and 4 days of culture, indicating decreased osteoblast precursor cell recruitment. Maintaining basal serum corticosterone levels in flight-ADX rats did not counteract the impaired bone formation in vertebral or pelvic bones. Moreover, the decreased ex vivo number of total and ALP+ endosteal bone cells induced by spaceflight occurred independent of endogenous corticosteroid hormone levels. These results indicate that the microgravity-induced inhibition of bone formation and resulting decreased trabecular bone mass in specific areas of weight-bearing skeleton in growing rats occur independently of endogenous glucocorticoid secretion.

Evaluation of apoptosis and the glucocorticoid receptor in the cartilage growth plate and metaphyseal bone cells of rats after high-dose treatment with corticosterone

A connection has been suggested between glucocorticoid-induced osteopenia and an increase in the apoptosis of bone cells, and between the dimerization of the glucocorticoid receptor (GR) and the development of apoptosis. On this basis, a study has been carried out on the relationships between the occurrence of apoptotic cells and their detectable GR content, and between apoptosis frequency and changes in histomorphometric variables, in the growth plate and secondary spongiosa of rat long bones after the high-dose (10 mg/day) administration of corticosterone (CORT) and after recovery. The main results of the CORT treatment were: a significant increase in apoptotic osteoblasts, and a concomitant decrease in the histomorphometric variables of bone formation, with a reversal of both values during recovery; a nonsignificant increase in the apoptosis of osteoclasts, without changes in the histomorphometric variables of bone resorption; a significant increase in apoptotic terminal hypertrophic chondrocytes; the presence of GR in all types of skeletal cells in control rats, with different (cytoplasmic and/or nuclear) immunohistochemical detection in the same type of cell; a decrease in GR detection in proliferative chondrocytes and osteocytes in CORT and recovery groups, and in the maturative/hypertrophic chondrocytes of the recovery group; a fall in growth cartilage width, possibly due to the reduced proliferation of proliferative chondrocytes and increased apoptosis in terminal hypertrophic chondrocytes. In conclusion, pharmacological doses of CORT reduce bone formation by increasing osteoblast apoptosis; they reduce growth cartilage width, probably by inhibiting chondrocyte proliferation and increasing the apoptosis of terminal hypertrophic chondrocytes, and they reduce osteocyte GR. Although these effects appear to be mediated by the presence of GR in all skeletal cells, no precise correlation between GR immunohistochemical detection and apoptosis induction has been found.

Estrogen prevents glucocorticoid-induced apoptosis in osteoblasts in vivo and in vitro

The ability of estrogen to prevent glucocorticoid-induced apoptosis in osteoblasts was studied both in vitro and in vivo. Glucocorticoid treatment for 72 h produced a dose-dependent increase in the number of apoptotic cells, determined by acridine orange/ethidium bromide staining, with a maximal response of 31+/-2% and 26+/-3% with 100 nM corticosterone in primary rat and mouse osteoblasts, respectively. Simultaneous administration of varying concentrations of 17beta-estradiol and 100 nM corticosterone decreased apoptotic osteoblasts in a dose-dependent manner, with a maximal decrease of 70% with 0.01 nM 17beta-estradiol. Terminal deoxynucleotidyltransferase-mediated deoxy-UTP-biotin nick end labeling also demonstrated glucocorticoid-induced DNA fragmentation that was inhibited by estrogen. Estrogen was shown to inhibit apoptosis induced by lipopolysaccharide treatment. As early as 6 h, Western blots demonstrated a dose-dependent decrease in the Bcl-2/Bax ratio, which reached a minimum of 0.18 in osteoblasts treated with 1000 nM corticosterone for 72 h. This reduction in Bcl-2/Bax was abolished by treating osteoblasts simultaneously with 17beta-estradiol, but not with 17alpha-estradiol. In 7-day-old mice, administration of varying concentrations of dexamethasone for 72 h resulted in a dose-dependent increase in the number of apoptotic osteoblasts as demonstrated by in situ terminal deoxynucleotidyltransferase-mediated deoxy-UTP-biotin nick end labeling staining of calvaria. A maximum of 22+/-1% apoptotic osteoblasts on the bone surface was found with 1 mg/kg BW dexamethasone compared with 2+/-1% in vehicle-treated mice. Injection of varying concentrations of 17beta-estradiol (0.5-5 mg/kg BW), but not 17alpha-estradiol, with 1 mg/kg dexamethasone produced a dose-dependent decrease in the number of apoptotic osteoblasts to 5+/-1% with 5 mg/kg 17beta-estradiol. Thus, glucocorticoid-induced apoptosis of osteoblasts may be prevented at least in part by 17beta-estradiol.

Growth hormone increases cortical and cancellous bone mass in young growing rats with glucocorticoid-induced osteopenia

The effects of growth hormone (GH) on linear growth, bone formation, and bone mass have been examined in glucocorticoid (GC)-injected young growing rats. Two-month-old female Wistar rats were injected for 90 days with 1, 3, 6, or 9 mg of methylprednisolone alone or in combination with 5 mg of GH. Bone mass and bone formation parameters were examined in the femoral cortical bone and in cortical bone and cancellous bone of the lumbar vertebra. GC administration dose dependently decreased growth, longitudinal growth of the vertebra, as well as the modeling drift of the cortical bone of the vertebral body and femoral diaphysis. In the vertebral cancellous bone, GC also decreased the mineralizing surface and inhibited the growth-related increase in cancellous bone volume. GH increased growth, longitudinal growth of the vertebra, as well as the modeling drift of the vertebral body and the femoral diaphysis, resulting in an increased cortical bone mass. GH also increased cancellous bone volume and the mineralizing surface of the vertebral body. In GC-injected animals, GH normalized and further increased growth, longitudinal growth, and the modeling drift of both the femoral diaphysis and the vertebral body, resulting in an increased cortical bone mass at both locations. GH also increased cancellous bone volume of the vertebral body in GC-injected animals, but GH did not, however, reverse the decreased mineralizing surface of cancellous bone induced by GC injections. In conclusion, GC administration to growing rats retards normal growth, longitudinal growth, and cortical bone modeling drift. It also decreases the cancellous bone mineralizing surface and inhibits the normal age-related increase in cancellous bone volume of the vertebral body. In the growing rat skeleton, GH can counteract these GC-induced side effects, except for the GC-induced decrease in the mineralizing surface of cancellous bone of the vertebral body, which remained unaffected by GH administration.

Prednisolone prevents decreases in trabecular bone mass and strength by reducing bone resorption and bone formation defect in adjuvant-induced arthritic rats

We examined the effects of prednisolone (PSL) administration in normal female Sprague Dawley rats and adjuvant-induced arthritic rats at the age of 6 weeks. Rats were intramuscularly injected with PSL twice a week at doses of 0 (control), 10, 30, 90, or 270 mg/kg body weight (b.w.). In the normal rats, serum osteocalcin level at 14 days and serum carboxyterminal pyridinoline cross-linked telopeptide of type 1 collagen (1CTP) level at 28 days in the 270 mg/kg dose group was lower than the respective value in control animals. The BMC and the trabecular bone formation rate (BFR/BS) of the lumbar body (L-4) in the 270 mg/kg dose group at 14 and 28 days were significantly lower than the values in the control rats. In the arthritic rats, however, serum osteocalcin levels in the PSL-treated groups did not differ compared with arthritic controls. The serum 1CTP levels in all of the PSL-treated groups were significantly reduced at 28 days. The age-dependent increases in the L4 BMC, BMD, and L-3 ultimate compressive load values were maintained. The BFR/BS values in the 90 mg/kg and 270 mg/kg dose groups were significantly higher than those in the arthritic control rats. The trabecular osteoclast number and surface values in all of the PSL-treated groups were significantly lower than the values in arthritic controls. These data demonstrate that PSL administration prevented reduction in bone mass and strength of the lumbar trabecular bone in adjuvant-induced arthritic rats by reducing the increase in bone resorption and the decrease in bone formation at both the local and systemic levels.

Inhibition of osteoblastogenesis and promotion of apoptosis of osteoblasts and osteocytes by glucocorticoids. Potential mechanisms of their deleterious effects on bone

Glucocorticoid-induced bone disease is characterized by decreased bone formation and in situ death of isolated segments of bone (osteonecrosis) suggesting that glucocorticoid excess, the third most common cause of osteoporosis, may affect the birth or death rate of bone cells, thus reducing their numbers. To test this hypothesis, we administered prednisolone to 7-mo-old mice for 27 d and found decreased bone density, serum osteocalcin, and cancellous bone area along with trabecular narrowing. These changes were accompanied by diminished bone formation and turnover, as determined by histomorphometric analysis of tetracycline-labeled vertebrae, and impaired osteoblastogenesis and osteoclastogenesis, as determined by ex vivo bone marrow cell cultures. In addition, the mice exhibited a threefold increase in osteoblast apoptosis in vertebrae and showed apoptosis in 28% of the osteocytes in metaphyseal cortical bone. As in mice, an increase in osteoblast and osteocyte apoptosis was documented in patients with glucocorticoid-induced osteoporosis. Decreased production of osteoclasts explains the reduction in bone turnover, whereas decreased production and apoptosis of osteoblasts would account for the decline in bone formation and trabecular width. Furthermore, accumulation of apoptotic osteocytes may contribute to osteonecrosis. These findings provide evidence that glucocorticoid-induced bone disease arises from changes in the numbers of bone cells.

Lack of effect of spaceflight on bone mass and bone formation in group-housed rats

As part of an experiment to study the role of corticosteroids in bone changes during spaceflight, male Sprague-Dawley rats (6 wk old, 165 g body weight) were placed in orbit for 17 days, in groups of six, in animal-enclosure modules (AEMs) aboard the space shuttle Columbia (STS-78). Control rats were group housed in a similar manner in ground-based AEMs or standard vivarium cages. Adrenal hypertrophy occurred in flight rats, but bone histomorphometric analyses revealed a lack of significant changes in bone mass and bone formation in these animals. Cancellous bone volume and osteoblast surface in the proximal tibial metaphysis were nearly the same in flight and ground-based rats. Normal levels of cancellous bone mass and bone formation were also detected in the lumbar vertebrae and femoral necks of flight rats. In the tibial diaphysis, periosteal bone formation rate was found to be identical in flight and ground-based rats. The results indicate that, under conditions of group housing in AEMs, spaceflight has minimal effects on bone mass and bone formation in rapidly growing rats. These findings emphasize the need to investigate the importance of rat age, strain, and especially housing conditions for studies of the skeletal effects of spaceflight.

Prednisolone alone, or in combination with estrogen or dietary calcium deficiency or immobilization, inhibits bone formation but does not induce bone loss in mature rats

Glucocorticoid use has long been recognized as a risk factor for bone loss, resulting in an increased fracture incidence in humans. However, steroid-treated patients often present with other complications that predispose to bone loss, such as immobilization, and little is known about the interaction of these other risk factors for bone loss and glucocorticoids. In the present study, mature female rats were treated with prednisolone (Pred) or vehicle, in combination with ovariectomy (ovx), dietary calcium deficiency (LoCa), or right hind limb immobilization (IM). After 4 weeks of treatment, the rats were killed and the right tibia and tibiofibular junction were collected for quantitative histomorphometric analysis and the right femur was collected for bone mineral density (BMD) and mechanical strength determinations. As expected, ovx, LoCa, and IM decreased BMD in the distal femur and cancellous bone volume (CnBV/TV) in the proximal tibia. All Pred-treated groups responded with increases of BMD and CnBV/TV, when compared to their respective non-Pred treated groups. Mechanical strength testing of the cancellous bone of the distal femur reflected the changes in BMD and CnBV/TV. No differences in trabecular plate thickness were noted in any of the treatment groups. The Pred group showed a significant reduction in longitudinal growth rate, as well as bone formation rate (BFR/BS), in the proximal tibia when compared with their respective control groups, the latter indicated by a decrease in both mineralizing surface and mineral apposition rate. Most notably, osteoclast surface and urinary free pyridinoline, a bone resorption marker, increased significantly with each of the three risk factors. Pred treatment inhibited these increases but it did not exert significant reductions when used by itself. At the tibiofibular junction, there were no measurable changes in either total bone or cortical bone area. Endocortical BFR/BS were increased by ovx or LoCa but each was lowered by Pred treatment. Periosteal BFR/BS were increased by ovx and IM, and Pred exerted significant inhibition by itself and in combination with other risk factors. We conclude, therefore, that unlike the effects observed in humans treated with glucocorticoid, treatment of rats with prednisolone not only does not result in bone loss but may exert a protective effect on the skeleton through the inhibition of bone resorption.

Decreased osteoblast activity in spontaneously diabetic rats. In vivo studies on the pathogenesis

Diabetes in both humans and rats is accompanied by low bone formation, which is presumably caused by serum-borne factors. To explore its pathogenesis, we carried out experiments in diabetic and nondiabetic BB rats, using plasma osteocalcin concentrations (OC) as a marker for osteoblast activity. In nondiabetic rats, the i.v. infusion of glucose (30%, 4 d) did not change OC; s.c. insulin infusion (4 U/d, 14 d) reduced OC by 27% (p < 0.01). In diabetic rats, OC were decreased from the first day of glycosuria (71 +/- 5% of paired controls), declining exponentially to 24 +/- 3% after 5 wk. Insulin infusion (1, 2, and 3 U/d, 14 d) produced gradual restoration of OC. OC were better correlated with insulin-like growth factor-I (IGF-I) than with insulin levels in these experiments. OC were dramatically increased 4 d after adrenalectomy (ADX) in all diabetic rats (73 +/- 8 vs 22 +/- 4 micrograms/L before ADX; p < 0.001), but not if corticosterone was administered. Ligand blotting of IGF binding proteins showed a marked decrease in two bands (44-49 and 32-35 kDa) 10-14 d after diabetes onset; the density of these bands was increased, but not normalized after ADX. Thus, decreased osteoblast activity is present from the onset of diabetes, is dependent on endogenous corticosterone, and cannot be reproduced by hyperglycemia in nondiabetic rats.

Calcium-lowering action of glucocorticoids in adrenalectomized-parathyroidectomized rats. Specificity and relative potency of natural and synthetic glucocorticoids

The specificity and potency of glucocorticoids to lower serum calcium (Ca) in rats after parathyroidectomy (PTX) and adrenalectomy (ADX) were examined. Rats fasted overnight were given sc injections of various steroids immediately after the operations. The fall in serum calcium 5 h after PTX-ADX in rats given hypocalcemic doses of corticosterone was compared to that after injection of a test steroid. At high doses, progesterone, estradiol, testosterone, and aldosterone were inactive, whereas glucocorticoids were consistently hypocalcemic. These results indicate that the Ca-lowering effect is specific for steroids with glucocorticoid activity. Potency estimates were made by comparing the dose-response of natural and synthetic glucocorticoids to that of corticosterone, the major glucocorticoid in rats. The mean potency of hydrocortisone was 8.2 times that of corticosterone. Prednisolone was about 9.6, triamcinolone 33, betamethasone 109, and dexamethasone 301 times as potent as corticosterone. Thus, the use of the calcium-lowering action as a bioassay has provides a specific and rapid in vivo method to compare potencies of glucocorticoids consistent with those obtained by anti-inflammatory and glycogen deposition assays. The importance of this interesting calcitonin-like action of glucocorticoids in normal physiology of calcium metabolism is not yet established.