Glucocorticoid-induced osteopenia in rats: histomorphometrical and microarchitectural characterization and calcitonin effect

Changes in osteocyte density correspond with changes in osteoblast and osteoclast activity in an osteoporotic sheep model

Histomorphometric assessment of trabecular bone in osteoporotic sheep showed that bone volume, osteoid surface area, bone formation rate, and osteocyte density were reduced. In contrast, eroded surface area and empty lacunae density were increased. Changes in osteocyte density correlated with changes in osteoblast and osteoclast activity.

INTRODUCTION

Osteocytes contribute to the regulation of the activity of osteoclasts and osteoblasts that together control bone mass. Osteocytes therefore likely play a role in the loss of bone mass associated with osteoporosis. The purpose of this study was to investigate the relationships between osteocyte lacunar density and other bone histomorphometric parameters in the iliac crest (IC) and lumbar spine (LS) of osteoporotic sheep.

METHODS

Osteoporosis was induced in ten mature ewes by an established protocol involving a combination of ovariectomy, dexamethasone injection, and low calcium diet for 6 months. Five ewes were used as controls. Post-mortem IC and LS biopsies were collected and processed for further histomorphometric assessment.

RESULTS

Bone volume, osteoid surface, and bone formation rate in the IC and LS of osteoporotic sheep were reduced compared to those of the controls. In contrast, eroded surface area was increased in osteoporotic sheep. In the osteoporotic group, osteocyte density was reduced in the LS region and to a greater extent in the IC region. The empty osteocyte lacunae were increased 1.7-fold in LS and 2.1-fold in IC in the osteoporotic group. The osteocyte density correlated positively with markers of osteoblast activity and negatively with those of osteoclast activity.

CONCLUSIONS

Depletion of osteocytes and an increase in the empty lacunae could be important factors contributing to bone loss in this model since they may adversely affect intercellular communication between osteoblasts and osteoclasts. The regional differences in histology suggest that there may be different pathological mechanisms operating at different anatomical sites.

Validation of the sheep as a large animal model for the study of vertebral osteoporosis

Rats have long been the animal of choice for research in the field of osteoporosis. In the search for a complementary large animal model the sheep appears useful but hitherto the extent of bone loss from the spine has failed to reach a level that is generally accepted as osteoporotic in humans. Osteoporosis was induced in ten sheep using ovariectomy, low calcium diet and steroid injection for 6 months. Bone samples of iliac crest (IC), lumbar spine (LS), and proximal femur (PF) from the osteoporotic sheep were compared with those from four normal sheep using densitometry, histomorphometry, biochemistry and basic mechanical testing. The differences were examined using an analysis of variance with Tukey-Kramer test. Overall, the bone mineral density at LS and PF decreased more than 25% after treatment. Trabecular bone volume decreased by 29.2, 33.4 and 42.6% in IC, LS and PF, respectively. The failure load of the LS in axial compression was reduced to 2,003 from 6,140 N. The extent of bone loss was sufficient to categorise these sheep as osteoporotic although the pattern of bone loss varied between sites. Reduced mechanical competence in LS confirmed the suitability of this model for evaluation of potential treatments for osteoporosis.

Influence of glucocorticoid on bone in 3-, 6-, and 12-month-old rats as determined by bone mass and histomorphometry

The influence of glucocorticoid (GC) on bone in rats at different ages was investigated in order to provide insight into human glucocorticoid induced osteoporosis (GCOP). Three-, 6-, and 12-month-old female Wistar rats were divided into four groups: Zero-time control (ZT), vehicle (Cont), prednisolone (PSL) 2 mg/kg (P-L), PSL 20 mg/kg (P-H). PSL was subcutaneously administered every day for 4 weeks. Bone mineral density (BMD) at the proximal metaphysis and diaphysis of the tibia was measured by peripheral quantitative computed tomography. Histomorphometry of the tibia was performed for 3- and 6-month-old rats. GC increased trabecular and cortical BMD at the metaphysis in all 3-month-old rats with time. Trabecular BMD at the metaphysis in the P-L and P-H groups was significantly higher than in the control group. Histomorphometric parameters for both bone formation and resorption were also increased by GC treatment. In the 6-month-old rats, the metaphyseal trabecular BMD did not significantly change in any group, but the diaphyseal trabecular BMD significantly increased in the control group with time. The trabecular BMD of the metaphysis and diaphysis was significantly lower in the P-L and P-H groups than in the control group at week 4. Histomorphometric parameters for bone formation and resorption were both reduced by GC treatment. The BMD remained unchanged in all 12-month-old rats. Six-month-old rats treated with 20 mg/kg GC are suitable models for GC-induced osteoporosis with dominant cancellous bone decrease and reduced bone turnover. The pathology induced by 20 mg/kg prednisolone in 6-month-old female rats seems to be most similar to glucocorticoid-induced osteoporosis in humans.

Risedronate prevents the loss of microarchitecture in glucocorticoid-induced osteoporosis in rats

Osteoporosis is a severe complication of glucocorticoid treatment. Bisphosphonates are a powerful therapeutic option to prevent osteoporotic fractures. The aims of this study were: a) to determine bone alterations induced by therapy with glucocorticoids (GC); b) to establish the efficacy of risedronate (Ris) in the prevention of these effects. We studied 40 female Sprague-Dawley rats randomly divided into 4 groups of treatment, administered 3 times a week sc: 1.

CONTROL

vehicle of methylprednisolone (GC) + vehicle of Ris; 2. Ris: Ris 5 mug/kg body weight vehicle of GC; 3. GC: GC 7 mg/kg + vehicle of Ris; 4. GC+Ris: GC 7 mg/kg, Ris 5 microg/kg. Animals were treated for 30 days and then were sacrificed. Densitometry was performed at baseline and at the end of the treatment. Right tibiae were removed for histomorphometric analyses. The GC group showed a 7% decrease in bone density vs controls (p<0.05), while the GC+Ris group was associated with a 3.5% increase in bone density vs controls (p<0.05). In the GC group, histomorphometric evaluations showed reduced bone volume (BV/TV) and thinning of trabeculae (Tb.Th) vs controls (BV/TV: 31+/-1 vs 35+/-1%, p<0.05; Tb.Th: 43+/-2 vs 50+/-3 microm, p<0.01; Ac.f: 1.8+/-0.2 vs 1.6+/-0.3 N/yr). The GC+Ris group had increased BV/TV and Tb.Th, and reduced Ac.f vs the GC group. Ris also maintained trabecular microarchitecture. At the histological level, glucocorticoid-induced osteoporosis was characterized by decreased bone volume, reduced osteoblastic activity, and deterioration of microarchitecture. Ris counteracted these effects both by prolonging osteoblast activity, and by maintaining bone microarchitecture.

Histomorphometric analysis of glucocorticoid-induced osteoporosis

Bone histomorphometry or quantitative histology consists of counting or measuring tissue components: cells, extracellular constituents and microarchitecture. Bone histomorphometry is the only method that allows the measurement of mineralization rate and the study of bone formation at three levels: cell, remodeling unit and tissue levels. It is a useful tool to explain the pathogenesis and cellular mechanisms of different metabolic bone diseases such as glucocorticoid-induced osteoporosis (GIO). Glucocorticoids (GC) affect calcium and bone metabolism at every level, but the main effect is the osteoblastic dysfunction. Concerning the bone formation, some histomorphometric studies have shown a depressed osteoblastic activity at a cell, bone remodeling unit, and tissue levels. In addition, there is evidence of a shortening of the period in which the osteoblasts work actively forming the bone matrix. This latter effect seems to occur after high cumulative doses of GC. With regard to the resorption, the results are still debated, but histomorphometric parameters seem to be increased in the majority of studies, at least in the first period of the GC treatment. From a structural point of view, GC seem to induce a thinning of the trabeculae without their perforation, which occurs only after high cumulative doses. Anti-resorptive treatments, such as bisphosphonates, are able to counteract the negative effects of GC on bone. In particular, along with their active working period, they prolong the lifespan of osteoblasts and osteocytes. In addition, the anti-resorptive treatments seem to extend the time for secondary mineralization through a reduction of the Activation Frequency. The latter is an intriguing mechanism of bisphosphonates in GIO that needs further ad hoc investigations.

Effects of vitamin K2 (menatetrenone) and alendronate on bone mineral density and bone strength in rats fed a low-magnesium diet

In this study, we examined changes in bone parameters and bone strength in rats fed low-Mg diets (experiment 1) and the effects of vitamin K2 (MK-4, experiment 3) and alendronate (ALN, experiment 2) in this model. In experiment 1, 5-week-old male Wistar rats were fed three low-Mg diets (Mg 9, 6, 3 mg/100 g diet) for 4 weeks. Although the cortical bone mineral content (CtBMC) and cortical thickness (CtTh) of the femoral diaphysis in all low-Mg-diet groups were the same as or greater than those in the intact group (Mg: 90 mg/100 g diet), the maximum load and elastic modulus were significantly reduced in the 3-mg-Mg group. In experiment 2, 4-week-old Wistar rats were fed a 6-mg-Mg diet for 8 weeks, and the effect of ALN (2, 20, and 200 microg/kg twice a week) was evaluated. The administration of ALN at 200 microg/kg increased the cortical bone mineral content (CtBMC), CtTh, and maximum load, but had no effect on the elastic modulus, as compared with the low-Mg-control group. In experiment 3, the effect of MK-4 was evaluated under the same conditions as in experiment 2. The administration of MK-4 had no effect on CtBMC, CtTh, or bone components of the femoral diaphysis. However, MK-4 inhibited the decreases in maximum load and elastic modulus due to the low-Mg diet. Since there is no other experimental model in which there is a decrease in bone mechanical properties without a decrease in bone mineral content, the low-Mg diet model is considered to be an excellent model for examining bone quality. Our results from this model suggest that MK-4 and ALN affect bone mechanical properties by different mechanisms.

Effect of Incadronate on Corticosteroid-induced Osteopenia in Rats

The effect of incadronate, a third-generation bisphosphonate, was evaluated in rats with corticosteroid-induced osteopenia. Male Wistar rats were treated with methylprednisolone acetate (1 mg/kg, s.c.) once daily, 3 days a week for 12 weeks. Other groups received simultaneous treatment with methylprednisolone acetate and incadronate (0.03, 0.3 or 3 mg/kg, p.o.); incadronate was given once daily, 6 days a week for 12 weeks. Bone mineral densities (BMDs) of the second lumbar (L2) vertebra as well as the ultimate compressive strength of the fifth lumbar (L5) vertebra decreased. Incadronate dose-dependently inhibited the loss of L2 BMDs and the decrease in strength of the L5 vertebrae. These results suggest that incadronate may be effective in treating osteopenia accompanying corticosteroid therapy.

Vitamin K2 (menatetrenone) inhibits bone loss induced by prednisolone partly through enhancement of bone formation in rats

Vitamin K(2) (K(2), menatetrenone) has been reported to enhance bone formation and inhibit bone resorption in vitro. However, there is no evidence that K(2) enhances bone formation in vivo. The aim of this study was to characterize the effect of K(2) on bone formation in vivo. We carried out two experiments using a prednisolone (pred)-induced bone loss model in male (10-week-old) Fischer rats. Pred was orally administered three times a week. In experiment 1, we compared the degree of bone loss induced by a 4 week treatment (30 or 100 mg/kg) and an 8 week treatment (3, 10, or 30 mg/kg) with pred by peripheral quantitative computed tomography (pQCT). At 4 weeks, total bone mineral density (BMD) was decreased only with the 100 mg/kg pred treatment. At 8 weeks, total BMD was significantly reduced at >10 mg/kg pred. In experiment 2, we investigated the effect of K(2) on bone loss induced by 3 and 30 mg/kg pred. K(2) (15 mg/kg) was given to rats as a dietary supplement for 8 weeks. Intestinal calcium transport (S/M) and total, trabecular, and cortical BMD at the metaphysis and diaphysis were measured, and histomorphometry was performed in diaphysial cross sections. Pred treatment decreased total and trabecular BMD in the proximal metaphysis. A decrease in cortical BMD in the diaphysis was observed in the pred 30 mg/kg group. Pred treatment also reduced mineralizing surface (MS/BS), mineral apposition rate (MAR), and bone formation rate (BFR/BS). The decrease in total and trabecular BMD in the proximal metaphysis, and in cortical BMD in the diaphysis, was inhibited by K(2) treatment. K(2) treatment also inhibited the decrease in MS/BS and BFR/BS induced by 30 mg/kg pred. These results suggest that K(2) prevents bone loss partly through the enhancement of bone formation.

Bone anabolic effects of PTH(1-34) and salmon calcitonin in ovariectomy- and ovariectomy-steroid-induced osteopenic rats: a histomorphometric and biomechanical study

Using an experimental model of type 1 osteoporosis under the chronic therapy with an anti-inflammatory steroid, the bone anabolic effect of PTH(1-34) was evaluated by histomorphometrical and biomechanical analysis. Wistar female rats (12-week-old) were ovariectomized and allowed to develop an osteopenic model in the presence or absence of methylprednisolone acetate (MPA: 0.1 mg/kg, s.c., 3-days-a-week basis from the 5th week after ovariectomy (OVX)). The osteopenia that developed for the first 12 weeks after OVX was almost completely normalized by subsequent PTH pulsing (20 microg/kg, s.c., 5-days-a-week) for 8 weeks starting at the 13th week; the following characteristics were observed: 1) proximal tibial metaphysis: recovered bone volume, rather increased trabecular thickness and osteoid volume, and normalized eroded surface; 2) 5th lumbar vertebra (L-5): partially recovered trabecular connectivity; 3) femur and 4th lumbar vertebra (L-4): recovered mechanical strength in maximum elastic load and maximum elastic energy. The anabolic effect of PTH(1-34) was not substantially modified by MPA. Salmon calcitonin (SCT: 10 U/kg per day, s.c., 5-days-a-week, for 8 weeks) was anabolic in limited parameters: decreased number of osteoclasts, recovered maximum elastic load in femur, and partially recovered maximum elastic load in L-4. The results suggest that PTH(1-34) pulsing is able to recover OVX-induced osteopenia in the structure and mechanical strength not only of the cancellous bone but also of the cortical bone, and the anabolic effect can be clinically expected even under steroid medication.

OP-1 for cervical spine fusion: bridging bone in only 1 of 4 rheumatoid patients but prednisolone did not inhibit bone induction in rats

We used OP-1 (also called BMP-7) on a collagen type-1 carrier in atlanto-axial posterior fusions to promote bony healing after wire fixation. 4 patients who had instability between the atlas and axis due to rheumatoid disease received the implants. The patients were examined with conventional radiography postoperatively at 2, 6 and 10 months. In 3 patients, no new bone formation was detectable. In 1 patient, new bone bridged the fusion site at 6 months. 3 patients were on chronic steroid treatment, including the patient in whom bone formation was detected. To determine whether steroid treatment could be responsible for the low rate of bone induction, 24 rats each received OP-1 implants in an abdominal muscle pouch. They were divided into 3 groups receiving saline, 0.1 or 1.0 mg/kg BW of prednisolone daily until they were killed 3 weeks postoperatively. Specimens were decalcified for histology and the amount of calcium in the decalcifying solution was measured. All groups showed ossicles induced by OP-1, and no effect of prednisolone was detected. Thus the failures in the patients may have causes other than prednisolone treatment.

Glucocorticoid-induced secondary osteopenia in female rats: a time course study as compared with ovariectomy-induced osteopenia and response to salmon calcitonin

Previously we reported that 8-week treatment with methylprednisolone acetate (MPA: 0.1 mg/kg, s.c., 3 days a week) of male rats caused a novel type of osteopenia whose development was prevented by salmon calcitonin (SCT) in a dose-dependent manner. In this study, to compare the MPA-inducible osteopenia with the ovariectomy (OVX)-inducible one, female rats were used instead of male rats and a time-course study of development was made. MPA treatments for 1, 2, 4 and 8 weeks histologically induced characteristic osteopenic changes in a time-dependent manner that were histomorphometrically detectable in tibiae within 4 weeks as reduced bone mass, accelerated bone resorption, and suppressed bone formation and mineralization. Node-strut analysis revealed that the connectivity of the trabecular structure remained unaffected. Such MPA-induced changes in the trabecular structure, to be defined as thinned-but-uncut, is in a good contrast with OVX-induced unthinned-but-cut structure, although the latter osteopenic changes became detectable 2 weeks earlier. Another previous finding confirmed herein was that MPA-induced osteopenia in female rats was also completely masked by SCT (10 U/kg, s.c., 5 days a week). The results indicate that the MPA-inducible secondary osteopenic model in either sex of rats would be usable for testing anti-osteopenic drugs.

Efficacy, safety and mechanism of cyclodextrins as absorption enhancers in nasal delivery of peptide and protein drugs

Cyclodextrins are used in nasal drug delivery as absorption enhancing compounds to increase the intranasal bioavailability of peptide and protein drugs. The most effective cyclodextrins in animal experiments are the methylated derivatives, dimethyl-beta-cyclodextrin and randomly methylated beta-cyclodextrin, which are active at low concentrations ranging between 2% and 5%. However, large species differences between rats, rabbits and humans exist for the nasal absorption enhancement by cyclodextrins. Based on toxicological studies of the local effects of cyclodextrins on the nasal mucosa dimethyl-beta-cyclodextrin and randomly methylated beta-cyclodextrin are considered safe nasal absorption enhancers. Their effects were quite similar to controls (physiological saline), but smaller than those of the preservative benzalkonium chloride in histological and ciliary beat frequency studies. In these studies, and in a study of the release of marker compounds after nasal administration, methylated beta-cyclodextrins were less toxic than sodium glycocholate, sodium taurodihydrofusidate, laureth-9 and L-alpha-phosphatidylcholine. Systemic toxicity after nasal cyclodextrin administration is not expected, because very low doses of cyclodextrins are administered and only very small amounts are absorbed. The mechanism of action of cyclodextrins may be explained by their interaction with the nasal epithelial membranes and their ability to transiently open tight junctions.

Short-term effects of corticosteroids on trabecular bone remodeling in old ewes

This study was an attempt to develop an animal model of steroid-induced low bone formation, potentially suitable for testing bone forming agents. The short-term effects of corticosteroids on bone remodeling were analyzed in ewes. One group of 16 animals (mean age: 9 +/- 1 years) received a daily intramuscular injection of 16 mg of methylprednisone (MP group) for 3 months. The other group of 16 animals was considered the control group. At the end of treatment, significant decreases of osteoblastic (-50%) and mineralizing (-64%) perimeters and wall width (-5%) were noted in the MP group. The bone formation rate at the tissue level was significantly decreased by 91%. In contrast, at the cell level, there was no reduction in the daily production of matrix by the osteoblasts: Aj.AR was 40% lower than in controls, but the difference was not significant. At the end of the treatment, a significant increase in eroded perimeter (+97%) was associated with a significant decrease of osteoclast number. Biochemical markers of bone formation (osteocalcin and bone-specific alkaline phosphatase) and urinary cAMP were unchanged. Due to the short duration of the treatment, neither bone volume nor microarchitecture parameters were modified. The decreases of both the activation frequency and osteoclast number associated with the increase in eroded surfaces suggest a prolongation of the reversal phase due to an inhibition of osteoblast differentiation. Changes of bone formation in ewes induced by short-term administration of MP were similar to those reported after 3 months of treatment in humans. Thus, corticosteroid-treated ewes may represent a suitable animal model of low bone formation.