Impact of antihypertensive therapy on postmenopausal osteoporosis: effects of the angiotensin converting enzyme inhibitor moexipril, 17beta-estradiol and their combination on the ovariectomy-induced cancellous bone loss in young rats

OBJECTIVE

No data are available on whether angiotensin converting enzyme (ACE) inhibition affects the skeleton, though this might be of clinical relevance when antihypertensive therapy is initiated, particularly in hypertensive women after menopause who typically suffer from a concomitant rapid onset of osteoporosis. In the present study we investigated the effects of the new ACE inhibitor moexipril, 17beta-estradiol and their combination on the bone turnover in ovariectomized Sprague-Dawley rats, an established animal model for studying human postmenopausal osteoporosis.

MATERIALS AND METHODS

We studied 119 12-week-old virgin female Sprague-Dawley rats. Seven rats were killed on day 0 as basal controls. The remaining rats were divided into sham-ovariectomy or ovariectomy groups. Vehicle, moexipril at 10 mg/kg per day alone (orally), 17beta-estradiol at 10 mu g/kg per day alone (subcutaneously) or both were administered to both groups immediately after the operation for 14 (short-term effects) or 56 (long-term effects) days. A stereology computer program was used for measurements. Static histomorphometric measurements, using a stereology computer program, were taken on double-fluorescent labeled undecalcified proximal tibial metaphyseal (cancellous bone site) and tibial shaft (cortical bone site) sections.

RESULTS

Ovariectomy induced dramatically cancellous bone loss due to increased bone turnover, with resorption exceeding formation. Moexipril had no effect on the cancellous bone site in either ovariectomized or sham-operated rats. 17beta-Estradiol treatment added extra cancellous bone in the sham-operated rats and prevented cancellous bone loss in the ovariectomized rats by inhibiting bone resorption. The combination of moexipril and 17beta-estradiol gave similar results to those of 17beta-estradiol alone. Comparable results were observed in the cortical bone site.

CONCLUSIONS

The results of this study show that ACE inhibition by moexipril has no effect on the skeleton when given alone and that it does not hamper the osteoprotective effects of 17beta-estradiol. These findings are relevant for the use of antihypertensive therapy in postmenopausal women treated or not with hormone replacement therapy.

Effects of prostaglandin E2 and F2 alpha on the skeleton of osteopenic ovariectomized rats

This article contains the histomorphometric evaluation of the effects of prostaglandin F2 alpha (PGF2 alpha) on cancellous bone from the lumbar vertebra and cortical bone from the tibial shaft of ovariectomized, osteopenic rats. These effects were then compared with those of prostaglandin E2 (PGE2). Three-month-old rats were either ovariectomized (ovx) or sham-ovx. Then, either PGF2 alpha or PGE2 in doses of 1 and 3 mg/kg/day was given subcutaneously for 21 days at 150 days post ovx. Histomorphometric analysis was performed separately on both the primary and secondary spongiosae of the fourth lumbar vertebral bodies (LVB) and on tibial shafts. The ovx rats exhibited osteopenia in both primary (-23% to -37%) and secondary (-20%) spongiosae of the LVB, but not in the tibial shafts at 150 and 171 days post ovx. In the LVB, PGE2 in doses of 1 or 3 mg/kg/day for 21 days restored trabecular bone volume to the levels of sham-ovx controls in the primary spongiosa. However, in the secondary spongiosa, the treatments only thickened the trabeculae. The effects of the PGF2 alpha treatment were similar to those of the PGE2 in both the primary and the secondary spongiosae. While both PGF2 alpha and PGE2 treatments stimulated bone formation in the LVB as indicated by the increases in labeled perimeter, tissue and bone area-based bone formation rates, PGE2 is about 10 times more potent than PGF2 alpha in these effects. The PGE2 treatment also elevated activation frequency in the LVB, while the PGF2 alpha treatment did not. The treatments differed in that PGE2 at these dose levels did not alter the eroded surface in the LVB while PGF2 alpha decreased it significantly. Thus, the increase of the ratio of labeled to eroded perimeter in the LVB in PGF2 alpha-treated animals was much more than that in PGE2-treated animals. In the tibial shafts, PGE2 in doses of 1 and 3 mg/kg/day produced new marrow trabeculae in 2 of 6 and 3 of 6 of the ovx rats. However, no new trabecula was found in PGF2 alpha-treated tibial shafts. Higher doses of PGE2 also increased periosteal labeled perimeter, MAR, and BFR/BS, while PGF2 alpha did not produce any significant change in these parameters. Both PGE2 and PGF2 alpha in doses of 1 and 3 mg/kg/day increased the labeled perimeter, MAR and BFR/BS and decreased the eroded perimeter in the endocortical surface. We concluded that both PGF2 alpha and PGE2 in doses of 1 and 3 mg/kg/day for 21 days exhibited anabolic bone effects. The effects were mostly confined to an increase in trabecular volume in the primary spongiosa of the LVB and in the endocortical surface of tibial shafts. The tissue level mechanism behind this appears to be that PGE2 and PGF2 alpha can both stimulate osteoblast recruitment and activity. Overall, we found PGE2 to be more potent than PGF2 alpha at the same dose level at the endocortical surface. Furthermore, new marrow trabecular bone formed only after PGE2 treatment. PGF2 alpha differed from PGE2 by significantly reducing the trabecular eroded surface in ovx rats.

Partial maintenance of extra cancellous bone mass by antiresorptive agents after discontinuation of human parathyroid hormone (1-38) in right hindlimb immobilized rats

The current study employs the immobilization (IM) rat model to induce osteopenia, parathyroid hormone (PTH) as the anabolic agent to restore bone mass, and 17 beta-estradiol, calcitonin, or risedronate as the maintenance agents to answer the following questions: How much cancellous bone loss occurs when PTH is withdrawn? Which antiresorptive or antiactivation agent maintains bone best? Ideally, what tissue-level histomorphometric conditions maintain added bone? Six-month-old female rats were treated with 200 micrograms PTH/day subcutaneously at 30 days post-IM for 75 days. Then PTH treatment was stopped and switched to a vehicle (no treatment), 10 micrograms calcitonin/kg/day, 10 micrograms 17 beta-estradiol/kg/day, or 5 micrograms risedronate twice weekly for another 15 days (early response) or 60 days (late response). The rats had their right hindlimb throughout the study. The current report deals only with the maintenance phase involving 92 animals. Bone histomorphometry was performed on the secondary spongiosa of the right proximal tibia metaphysis (PTM). Cessation of PTH treatment followed by vehicle administration for 15 days resulted in partial loss of trabecular bone area and thickness from stimulated bone resorption and the fall of all formation indices. By contrast, all three antiresorptive agents maintained the cancellous bone mass during the same period. However, after prolonged withdrawal of PTH for 60 days, we found that 17 beta-estradiol and calcitonin maintained the cancellous bone slightly better than no treatment, while risedronate partially protected it from the mechanostat-induced bone loss. The risedronate treatment retained 71% of the PTH-added bone while calcitonin retained 48%, estrogen 42%, and no treatment 32%. The favorable histomorphometry profile for maintenance was the sustained reduction in bone resorption and turnover and normal age-related bone balance. We concluded that 1) cessation of PTH treatment will result in the loss of two-thirds of the added bone in 60 days; 2) currently, risedronate at the dose level employed as a maintenance agent is far superior to 17 beta-estradiol or calcitonin because of its long retention in bone; however, a longer observation period might result in less difference; and 3) the ideal tissue-level histomorphometry continues depressing bone resorption and turnover and maintains a normal age-related bone balance. Furthermore, we found the "lose, restore plus add, and maintain (LRAM)" concept was successful in maintaining most of the PTH-induced extra bone by risedronate for 60 days. It was far superior to 17 beta-estradiol or calcitonin. Possibly the last two agents would be effective in maintaining a normal amount of bone but not in preserving an excessive amount of bone. Nevertheless, the current study further emphasizes that clinicians should consider using the LRM treatment strategy when they plan to treat osteoporosis with bone anabolic agents.

Effects of droloxifene on prevention of cancellous bone loss and bone turnover in the axial skeleton of aged, ovariectomized rats

The purpose of this study was to determine the efficacy of droloxifene (DRO), an estrogen antagonist/agonist, in preventing ovariectomy (OVX)-induced lumbar vertebral cancellous bone loss and bone turnover in aged female rats. Fifty-three Sprague-Dawley female rats were OVX or sham-operated at 19 months of age, and divided into 6 groups: (I) sham-operated controls; (II) OVX vehicle controls; (III) OVX rats treated with E2 at 30 micrograms/kg/day; (IV)-(VI) OVX rats treated with DRO at either 2.5, 5, or 10 mg/kg p.o. daily. The treatment period was 8 weeks. Static and dynamic cancellous bone histomorphometric parameters were determined on 4 and 10 microns thick, undecalcified, double-fluorescent labeled sections of the fourth lumbar vertebral body. Changes in body weight, uterine weight, and total serum cholesterol were also determined. OVX for 8 weeks in 19-month-old female rats resulted in reduced trabecular bone volume (-18%) and trabecular width (-10%) and increased labeling perimeter (+52%), bone formation rate/bone surface referent (+60%), bone formation rate/bone volume referent (+77%), osteoclast number (+41%), and osteoclast perimeter (+41%). E2 treatment at 30 micrograms/kg/day for 8 weeks prevented OVX-induced cancellous bone loss and decreased bone resorption, bone formation, and bone turnover to the values of sham controls. DRO at 2.5-10 mg/kg/day completely prevented bone loss and bone turnover associated with estrogen deficiency. Osteoclast number and perimeter were significantly decreased in DRO-treated-OVX rats compared to both sham and OVX controls. Trabecular bone volume, trabecular width, labeling perimeter, bone formation rate/bone surface referent, and bone formation rate/bone volume referent showed no differences in DRO-treated OVX rats compared to those of E2-treated OVX rats and sham controls. These histomorphometric results indicated that DRO is an estrogen agonist on cancellous bone of lumbar vertebral bodies of aged, OVX rats. Further, E2 treatment prevented the OVX-induced increase in body weight gain and nonsignificantly reduced total serum cholesterol compared to OVX controls. Body weight gain and total serum cholesterol did not differ between OVX rats treated with E2 and sham controls. In OVX rats treated with DRO, body weight decreased significantly in a dose-response manner, and total serum cholesterol was significantly reduced by 65% to 70% compared to both sham and OVX controls. In addition, treatment with E2 increased uterine weight to the value of sham controls in OVX rats. However, DRO had no effect on uterine weight at either 2.5 or 10 mg/kg/day, while it only slightly but significantly increased uterine weight over OVX controls at 5 mg/kg/day. We conclude that DRO was efficacious in the prevention of lumbar vertebral cancellous bone loss and in the decline of total serum cholesterol but had no effect on uterine weight in the aged, OVX female rats. Our data suggest that DRO is a potentially useful agent for the prevention of vertebral bone loss leading to spinal fractures in postmenopausal women.

Intermittent treatments of prostaglandin E2 plus risedronate and prostaglandin E2 alone are equally anabolic on tibial shaft of ovariectomized rats

Effects of intermittent administration of prostaglandin E2 (PGE2), risedronate (Ris) and their combination on bone mass were studied on the cortical bone of tibial shafts of ovariectomized (ovx) rats. Six month old ovx rats were treated immediately after operation with subcutaneous injections of 6 mg PGE2/kg/d, 5 micrograms Ris/kg/2x/wk or their combination for 60 days each of an on/off/on cycle. PGE2 alone and in combination with Ris added the same amount of new bone in the first 60 days on period. During the 60 days off period, newly added endocortical and marrow trabecular bone disappeared in PGE2 alone treatment groups. In co-treatment group, the marrow trabeculae were only partly lost. There was no difference in total bone area between co-treatment and PGE2 alone groups after another 60 days on treatment. Our findings indicate that co-treatment was better in the maintenance of newly added endocortical and marrow trabecular bone during the off period; however, it formed less bone than PGE2 alone during the second treatment period, and ended up with the same amount of bone with both treatments.

Tomographic (pQCT) and biomechanical effects of hPTH(1-38) on chronically immobilized or overloaded rat femurs

Six-month old rats chronically submitted to right hindlimb immobilization (IM) with mechanical overload (OL) of the left leg were treated 1 month later with 200 micrograms/kg/d of hPTH(1-38) for 15 or 75 days. Peripheral quantitative computed tomography (pQCT) scans and bending tests showed that hPTH increased cortical mass and volumetric BMD (vCtBMD) in both legs. However, elastic modulus of cortical bone and diaphyseal load-bearing capacity were improved only in OL bones. Improvement of diaphyseal strength was attributable to that of cortical bone quality, yet a stronger mechanostatic response of cortical modeling to bone material quality was also observed in treated OL bones. Data support hPTH(1-38) use for improving cortical bone mass and strength and point out a physical activity interaction with therapeutic results.

Available animal models of osteopenia--small and large

Animal models of osteopenia are reviewed. Endocrine excess or deficiency conditions include ovariectomy, orchidectomy, glucocorticoid excess and other endocrine states. Seasonal and reproductive cycles are usually transient and include pregnancy and lactation, egg-laying, antler formation and hibernation. Dietary conditions include calcium deficiencies, phosphate excess and vitamin C and D deficiencies. Mechanical usage effects include skeletal underloading models. Aging is also associated with osteopenia in many species.

Bone mineral metabolism in T lymphocyte-deficient and -replete strains of rat

The immune and skeletal systems are known to interact. We have repeatedly shown that in contrast to in vitro data, the administration of T lymphocyte immunosuppressants, such as cyclosporin A, leads to an increase in bone resorption and a high turnover osteopenia. The purpose of this study was to characterize the bone metabolism of the T lymphocyte deficient Rowett athymic homozygous (rnu/rnu) nude rat. We wished to determine whether these rats share the bone abnormalities of cyclosporin A-treated rats. Eleven 10-week-old Sprague-Dawley rats and 12 similarly aged nude rats were studied over a 4-week period. Metaphyseal cancellous bone histomorphometry was similar in the two groups of rats and only differed with regard to percentage eroded perimeter (lower in nude rats, p = 0.0008) and longitudinal growth rate (49% lower in nude rats, p < 0.001). The nude rats had less body mass (p < 0.001) but nevertheless gained the same percentage of their body weight over the study period. The athymic rats had lower levels of serum, 1,25-dihydroxyvitamin D (p < 0.014) and serum osteocalcin(p < 0.009), and at the age of 14 weeks the nude rats had lower concentrations of serum creatinine (p = 0.001) and blood ionized calcium (p = 0.0002), yet serum PTH was similar throughout. RNA isolated from the contralateral tibias revealed that the nude group had lower steady-state levels of osteocalcin mRNA despite similar rates of bone formation. In its entirety, the data suggest that T cell deficiency per se is not necessarily associated with high turnover osteopenia.

Risedronate plus prostaglandin E2 is superior to prostaglandin E2 alone in maintaining the added bone after withdrawal in a non-growing bone site in ovariectomized rats

Effects of risedronate and prostaglandin E2 (PGE2) alone or in combination on the distal tibia, a non-growing bone site with closed epiphysis at 3 months of age, were studied in ovariectomized (ovx) rats. Six-month-old Sprague-Dawley female rats were either ovx or sham-ovx. Rats were treated immediately after operation either with risedronate (5 micrograms/kg/2x/wk), PGE2 (6 mg/kg/d), or risedronate+PGE2 for 60 days (on-groups) and followed by 60 days without treatment (off-groups). Trabecular area, width and numbers were determined in metaphyseal cancellous bone of the distal tibia. No significant bone loss or structural changes were observed in the distal tibial metaphysis after 120 days of ovx. Risedronate alone did not produce any effect on bone mass during the treatment and the withdrawal periods. PGE2 alone increased the trabecular bone mass associated with thickened trabeculae and increased trabecular numbers. However, some of the newly formed bone was lost at the end of 60 days withdrawal. Combination of risedronate and PGE2 treatment added the same amount of bone mass as PGE2 alone, and the added new bone was maintained during the 60 days withdrawal. These results indicate that treatment with risedronate and PGE2 can preserve the anabolic effect of PGE2 on bone mass for at least 60 days after treatment.

Intermittent treatment of prostaglandin E2 with risedronate is more anabolic than prostaglandin E2 alone in the proximal tibial metaphysis of ovariectomized rats

This study is designed to test how intermittent application of prostaglandin E2 (PGE2) and risedronate (Ris) alone or in combination acts on the cancellous bone mass in estrogen-deficient rats. Sprague-Dawley rats were ovariectomized (ovx) or sham-ovx'd at 6 months of age. PGE2 (6mg/kg/d), Ris (5 micrograms/kg/twice a week) or PGE2 plus Ris were given for 60 days to ovx rats immediately after operation and followed by 60 days without treatment. The drugs were then reapplied for another 60 days. Static histomorphometry was performed on the secondary spongiosa of proximal tibial metaphysis (PTM). Sixty days of ovx lost trabecular bone and number, Ris prevented ovx-induced bone loss. PGE2 added 48% extra cancellous bone, but the new bone was completely lost after 60 days of withdrawal. Another 60 days of PGE2 treatment only partially restored the trabecular bone, the bone mass was still -42% lower than that of sham-ovx controls. Co-treatment of PGE2 with Ris added the same amount of bone as PGE2 alone after the first 60 days treatment period, but differed from PGE2 alone in that the new bone lost less during the 60 days withdrawal period. Re-application of co-treatment for another 60 days added more extra bone. We concluded that intermittent co-treatment with anabolic and anti-resorptive agents is more effective than anabolic agent alone in long-term therapy of cancellous bone in estrogen-deficient rats.

Parathyroid hormone therapy accelerates recovery from immobilization-induced osteopenia

Previous reports have shown that bone mass and architecture will partially recover by remobilization (RM) in immobilization (IM)-induced osteopenia. The aim of this study was to test whether PTH can accelerate the recovery during RM from the IM-induced osteopenia. Six-month-old Sprague-Dawley female rats were divided into aging and IM groups. The right hindlimb of rats was immobilized against the abdomen by elastic bandages for 18 weeks, then groups of rats were further IM or RM for 2, 10 and 20 weeks and given 30 or 80 micrograms hPTH (1-38)/kg/d s.c. Secondary spongiosa of proximal tibial metaphyses (PTM) were studied. Immobilization reduced the trabecular area, number and thickness at the first 18 weeks post IM, then plateaued. Ten weeks of RM restored 40% trabecular bone from IM controls due to thickening of the trabeculae. However, the trabecular area was still -14% and -13% lower than that of aging controls at 10 and 20 weeks. Two weeks of 30 micrograms PTH/kg/d in IM rats restored the bone to aging control levels, two weeks of 30 micrograms PTH/kg/d in RM rats and of 80 micrograms PTH/kg/d in both RM and IM rats added extra bone. Extending the treatment to 10 and 20 weeks, the same amount of total bone was added to both IM and RM rats. These findings indicate PTH is a powerful agent that can accelerate the recovery and add extra bone to osteopenic cancellous bone in both IM and RM rats.

Remobilization partially restored the bone mass in a non-growing cancellous bone site following long term immobilization

There is no report in the rat of the effects of remobilization (RM) in an adult bone site. The aim of this study was to determine whether complete recovery from IM-induced bone loss will occur in a non-growing bone site, the distal tibia. Seventy-five 6-month-old virgin Sprague-Dawley female rats were used in this study. Their hindlimbs were immobilized against the abdomen with bandages for 18 weeks, then remobilized for 2, 10 or 20 weeks. Distal tibial sections were analyzed in the former epiphysis, 0.3 mm proximal from the calcified cartilage, and in trabecular bone of the former metaphysis between 0.3 mm and 1.92 mm proximal to the former epiphysis. A significant bone loss occurred in both former epiphyseal and metaphyseal trabeculae at 18 weeks after IM. The lost bone was partially recovered at 10 weeks of RM, but the bone mass was still lower than in aging controls by the end of the study. The partial recovery was characterized by decreasing former epiphyseal bone porosity and thickening of former metaphyseal trabeculae with no effect on trabecular number. We concluded that both distal tibia regions only partially recovered, during 20 weeks of RM from the long time IM.

Maintenance therapy for added bone mass or how to keep the profit after withdrawal of therapy of osteopenia

Since continuous therapy for osteoporosis can be expensive and may have detrimental effects, there is a need to develop a strategy to maintain bone mass after withdrawal of treatment. The bone maintained by estrogen and calcitonin therapies and exercise, but the added bone induced by anabolic agents disappears upon cessation of treatment. To avoid this pitfall, the concepts of activation, restore and maintain (ARM) or loss, restore and maintain (LRM), the on/off administration of combined anabolic agent with an antiresorptive or antiactivation agent, and cyclical treatment of the two regimes have been employed successfully in "keeping the profit" (maintaining bone) in preclinical studies. The data for the disappearance of bone upon cessation of certain osteopenic treatments, its mechanism of loss and the development of maintenance concept and subsequent preclinical studies indicate that there was no need for costly continuous therapy in the treatment strategy for osteoporosis.

Effects of on/off anabolic hPTH and remodeling inhibitors on metaphyseal bone of immobilized rat femurs. Tomographical (pQCT) description and correlation with histomorphometric changes in tibial cancellous bone

An anabolic effect of hPTH(1-38) (s.c. doses of 200 micrograms/kg/d during 75 days) on trabecular and cortical bone mass is tomographically described in the metaphyseal region of immobilized rat femurs using pQCT technology, in agreement with previous histomorphometrical studies of the proximal tibial metaphyses. Correlations between pQCT and histomorphometrical data showed that this effect derived from a stimulation of endosteal and trabecular bone modeling that induced a transference from trabecular to cortical bone mass. Loss of effects after withdrawal, resulting from a stimulation of bone remodeling, could be total or partially prevented by subsequent s.c. injections of risedronate (5 micrograms/kg/2/wk), 17-B-estradiol (10 micrograms/kg/d) or calcitonin (10 micrograms/kg/d) given during 60 days, in this order of effectiveness. The preventive potency was proportionally related to the reduction induced in histomorphometric indices of bone resorption.

Adaptation of non-growing former epiphysis and metaphyseal trabecular bones to aging and immobilization in rat

No data exit for distal tibia (DT), a bone site with growth plate closure at 3 months of age and with very low trabecular bone turnover rate. The purpose of this study was to characterize the response of DT to aging and immobilization (IM) in 6 to 16.5 month-old female rats. One hundred and forty six 6 month-old Sprague-Dawley rats were divided into aging controls and right hindlimb immobilization (RHLI) groups. The right hindlimb was immobilized against the abdomen with elastic bandages. Rats were sacrificed serially from 6 to 16.5 months old at intervals of 2 to 8 weeks. The histomorphometric study was performed on areas of former epiphyseal and metaphyseal trabecular bone of DT. No changes on bone mass or architecture were found in aging controls throughout the study. There was a decrease in bone mass of the former epiphysis after 3.5 months of IM due to resorption exceeding formation. Then it reverted to the aging control level at 4 months post IM. At the former metaphyseal site, significant bone loss (-19%) was observed as early as two weeks after IM. The peak bone loss (-54%) was reached at 1.5 months after IM and plateaued thereafter. The bone loss was mainly due to the reduction of trabecular thickness although trabecular number decreased significantly after 3.5 months IM. These results suggest that both former epiphysis and metaphyseal trabecular bones in DT can quickly adapt by losing bone to immobilization.

Risedronate pretreatment does not hamper the anabolic effects of prostaglandin E2 in ovx rats

Pretreatment of an anti-resorptive agent on the anabolic effects of prostaglandin E2 (PGE2) was studied on the proximal tibia and tibial shaft of ovariectomy (ovx) rats. Two days after ovx, rats were treated with either risedronate (Ris, 5 micrograms/kg twice weekly) or vehicle (V) for 60 days and then switched to 3 or 6 mg/kg/d PGE2 for 21 or 90 days. Bone area of both proximal tibial metaphysis (PTM) and tibial shaft (TX) were measured. Pretreatment with Ris increased the bone mass in PTM but not in TX of ovx rats. In the PTM, PGE2 produced the same percentage of new bone mass in both V- and Ris-pretreated ovx rats. The amount of new bone was almost the same after 3 weeks and 12 weeks of PGE2 treatment. There was no difference in the anabolic effects of 3 and 6 mg PGE2/kg/d in V-pretreated rats; however, the effects in Ris-pretreated groups were greater with 6 mg PGE2/kg/d than with 3 mg PGE2/kg/d. In TX, only the 6mg PGE2/kg/d administration added new bone on endocortical surfaces of both V- or Ris-pretreatment rats which leads to thickening the minimal cortical width, decreasing the marrow cavity and increasing total bone area. Both doses of PGE2 created new trabecular bone in the marrow cavity of tibial shaft in both vehicle- and Ris-pretreated ovx rats. These results suggest that Ris-pretreatment did not hamper the anabolic effects of PGE2 on either PTM or TX in ovx rats.

Droloxifene inhibits cortical bone turnover associated with estrogen deficiency in rats

Droloxifene (DRO), an estrogen antagonist/agonist, has been shown to possess estrogen-like effects in inhibiting bone turnover leading to cancellous bone loss in ovariectomized (OVX) rats. The purpose of this study was to determine the effects of DRO on cortical bone turnover in OVX rats. Sprague-Dawley female rats at 5 months of age were sham-operated (sham, n = 8) and orally treated with vehicle, or OVX (n = 56) and orally treated with either vehicle, DRO at 0.1, 1, 5, or 10 mg/kg/day, or 17 alpha-ethynyl estradiol (EE) at 3 or 30 micrograms/kg/day for 4 weeks. Static and dynamic cortical bone histomorphometry was performed on double fluorescent labeled, undecalcified cross sections of tibial diaphyses (proximal to the tibiofibular junction). There were no significant differences in tibial diaphyseal cross sectional area, marrow cavity area, and cortical bone area between groups after 4 weeks of administration. Periosteal mineralizing surface, mineral apposition rate, and bone formation rate-surface referent and endocortical eroded surface increased significantly, while endocortical mineral apposition rate and bone formation rate-surface referent increased nonsignificantly in OVX controls compared to sham controls. Treatment with DRO at doses of 0.1 to 10 mg/kg/day dose-dependently attenuated the OVX-induced higher bone formation indices in both the periosteal and endocortical surfaces and higher bone resorption index in the endocortical surface. At the highest dose (10 mg/kg/day), DRO completely inhibited the increases in bone formation and resorption indices in OVX rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Early effects of prostaglandin E2 on bone formation and resorption in different bone sites of rats

The aim of this study was to determine early effects of prostaglandin E2 (PGE2) on bone mass, formation and resorption in a growing cancellous bone site (the proximal tibial metaphysis, PTM), non-growing cancellous bone site (the distal tibial metaphysis, DTM), and cortical bone site (the tibial shaft, TX) with histomorphometric analysis. Six mg PGE2/kg/d was given s.c. to 6-month-old Sprague-Dawley female rats for 5, 10 or 16 days. Double fluorescent labels were given to 0, 10- and 16-day PGE2 treatment and 16-day control groups. Significant increase in bone mass was found after 16 days treatment in cancellous bone sites but not in the cortical bone site. Stimulated bone formation, indicated by the increase in osteoid perimeter, was observed as early as 5 days post-treatment in all 3 bone sites. Bone formation indices were increased after 10 days of treatment, however, there was no difference in selected bone formation indices between 10 and 16 days PGE2 treatments at all 3 bone sites. Significant increase in eroded surface and eroded surface covered with osteoid was observed in cancellous bone sites after 5 days, but decreased after 10 days of treatment. Although the eroded surface was not elevated in TX at the 5th day, the eroded surface covered with osteoid was increased on endocortical surface which indicated that PGE2 stimulated bone resorption on this surface prior to day 5. We concluded that PGE2 stimulated the bone formation and resorption as early as 5 days post-treatment. The levels of stimulated bone formation was TX > DTM > PTM.(ABSTRACT TRUNCATED AT 250 WORDS)

An in-vivo model for the rapid assessment of skeletal effects of anabolic agents

We recently developed an in vivo model which can be used to rapidly assess the local skeletal effects of anabolic agents. In this model, 160 g Sprague-Dawley (SD) rats were used. A stainless steel cannula was inserted into the marrow cavity of the proximal tibia through the anterior-medial cortex 6 mm distal to the knee joint. The outer opening of the cannula was covered by skin. Agents with known anabolic skeletal effects or vehicle were injected daily for 10 days into the marrow region by a small needle passing through the cannula. Rats were also injected subcutaneously with a fluorescent bone marker to label the newly formed bone. Injection sites were fixed, embedded, and sectioned for histomorphometric analysis of trabecular bone. PTH and PGE2 stimulated a large amount of new trabecular bone formation in regions proximal and distal to the injection site as measured by histomorphometry. Control groups showed minimal bone formation, limited to formation of a thin layer of bony shell immediately surrounding the cannula. The profound anabolic skeletal effects of PTH and PGE2 seen in this Local Injection Model are similar to those seen in systemic injection (i.e. subcutaneous injection in intact or castrated male and female rats) previously reported. This Local Injection Model combines numerous advantages of in vivo models (systemic injection) and in vitro models when assessing agents with anabolic skeletal activities. Compared to conventional in vivo systemic injection models, this model enables detection of anabolic skeletal effects using very small quantities (in microgram) of test agents in a short treatment period (< 10 days).(ABSTRACT TRUNCATED AT 250 WORDS)

Co-treatment of PGE2 and risedronate is better than PGE2 alone in the long-term treatment of ovariectomized-induced osteopenic rats

We studied the effects of prostaglandin (PGE2) and risedronate (Ris) alone or in combination in 3.5-month-old intact and ovx-induced osteopenic rat skeletons to determine whether PGE2 plus Ris was more anabolic than PGE2 alone. Six mg PGE2/kg/d and 5 micrograms Ris/kg/2x/wk alone or in combination were given to sham-ovx and ovx rats for 30 or 90 days beginning 60 days post operation. Secondary spongiosa of proximal tibial metaphyses (PTM) was studied. Ovariectomy (ovx) induced dramatic bone loss. Ris increased bone mass in sham-ovx rats and prevented further bone loss in ovx rats. PGE2 treatment for 30 days added extra bone in sham-ovx rats and no further increase after 90 days treatment. Thirty days of PGE2 alone treatment restored the bone mass in ovx rats to the level of sham-ovx rats, but the restored bone was partially lost by 90 days of treatment. Co-treatment for 30 days produced the same amount of bone mass in both sham-ovx and ovx rats as PGE2 alone did. However, unlike the PGE2 alone treated, co-treatment animals continued to form more bone for 90 days. The difference in tissue-level histomorphometry between co-treatment and PGE2 alone was that the former depressed the bone resorption and turnover. These findings indicated that the long-term administration of PGE2 alone cannot maintain or continue to add bone mass in ovx rats but that co-treatment of a PGE2 with an anti-resorptive or activation agent can resist the influence of the mechanostat induced bone loss as well as continue to add bone.

Droloxifene prevents ovariectomy-induced bone loss in tibiae and femora of aged female rats: a dual-energy X-ray absorptiometric and histomorphometric study

Our previous studies indicated that droloxifene (DRO), a tissue-specific estrogen antagonist/agonist, prevented bone loss without causing uterine hypertrophy in growing ovariectomized (OVX) rats. Using dual-energy X-ray absorptiometry (DXA) and bone histomorphometry, the current study compared the efficacy of DRO to 17 beta-estradiol (E2) in preventing OVX-induced bone loss in tibiae and femora of 19-month-old rats to determine whether DRO had similar skeletal effects as E2 in aged female rats. Sprague-Dawley female rats were OVX or sham-operated (sham) at 19 months of age. The sham-operated rats were treated with vehicle (oral), while the OVX rats were treated with vehicle (oral), E2 at 30 micrograms/kg/day (sc), or DRO at 2.5, 5, or 10 mg/kg/day (oral) for 8 weeks. Bone mineral density (BMD) of whole femora (WF), distal femoral metaphyses (DFM), femoral shafts (FS), and proximal femora (PF) was determined using DXA. Static and dynamic cancellous bone histomorphometric analyses were performed in double-labeled undecalcified longitudinal sections from proximal tibial metaphyses. Ovariectomy for 8 weeks significantly reduced the BMD of WF, DFM, FS, and PF (from -6 to -15%). Treatment with E2 completely prevented the decreases in BMD of WF and DFM and had no significant effects in BMD of FS and PF in aged OVX rats. The decrease in BMD of DFM induced by OVX was prevented by treatment with DRO at all dose levels. In addition, DRO at 10 mg/kg/day prevented OVX-induced decreases in BMD of WF, FS, and PF.(ABSTRACT TRUNCATED AT 250 WORDS)

Extra cancellous bone induced by combined prostaglandin E2 and risedronate administration is maintained after their withdrawal in older female rats

Prostaglandin E2 (PGE2) has been recognized for its marked anabolic effect on bone, but the bone gain is lost after the cessation of PGE2 treatment. In previous studies, we were successful in maintaining the new bone by administering a bisphosphonate after the withdrawal of PGE2 treatment. The objective of this study was to determine the fate of the extra bone induced by a combination with PGE2 and risedronate after discontinuing treatment. Ninety-six 9-month-old virgin female Sprague-Dawley rats were treated with 1 or 5 micrograms of risedronate/kg/twice weekly, 6 mg of PGE2/kg/day alone or 6 mg of PGE2/kg/day plus 1 or 5 micrograms of risedronate/kg/twice weekly for 60 days (day 0) and followed by 60 days without treatment (day 60). We have reported the results from the groups treated for 60 days previously. This report is restricted to the histomorphometric findings on the secondary spongiosa of the proximal tibial metaphysis in the groups after withdrawal for 60 days. We found that the only group that maintained the PGE2 induced new bone after withdrawal was the group treated with 6 mg of PGE2/kg/day plus 5 micrograms of risdronate/kg/twice a week. Withdrawal of this combined treatment depressed bone turnover (bone-based bone formation rate, activation frequency) and bone resorption (percent eroded perimeter). The tissue mechanisms responsible for the protection drew from the previously deposited risedronate.

Rapamycin: a bone sparing immunosuppressant?

Immunosuppressant therpay is associated with osteoporosis both clinically, post-transplantation, and experimentally. In rats, cyclosporin A (CsA) and FK506 induce a state of high turnover rapid bone loss. After 14 days of administration in immunosuppressive doses, the more recently discovered immunosuppressant, rapamycin, resulted in no change of cancellous bone volume. A longer study over 28 days has now been carried out; contrasting the new drug with CsA and FK506. Sixty, 10-week-old Sprague-Dawley rats were randomly divided into five groups of 12 rats each. The first group served as an aging control. The remaining four groups received, by daily gavage, a combined vehicle placebo, CsA 15 mg/kg, FK506 5 mg/kg, and rapamycin 2.5 mg/kg, respectively. CsA- and FK506-treated rats, but not those treated with rapamycin, demonstrated high turnover osteoporosis with raised serum 1,25(OH)2D (p < 0.05) and elevated serum osteocalcin (p < 0.05). The trabecular bone area was decreased by 66% (p < 0.01) in the CsA group and 56% (p < 0.05) in the FK506-treated group compared with the control animals. The CsA- and the rapamycin-treated groups failed to gain weight and developed severe hyperglycemia (> 20 mmol/l, p < 0.001) by day 14 but which largely resolved by day 28. Unlike the groups treated with CsA and FK506, rapamycin-treated rats had no loss of trabecular bone volume but there was increased modeling and remodeling and a decreased longitudinal growth rate. Rapamycin may thus confer a distinct advantage over the established immunosuppressants in not reducing bone volume in the short term.(ABSTRACT TRUNCATED AT 250 WORDS)

Human parathyroid hormone-(1-38) restores cancellous bone to the immobilized, osteopenic proximal tibial metaphysis in rats

The purpose of this study was to determine if human parathyroid hormone-(1-38) (hPTH(1-38)) can restore cancellous bone mass to the established osteopenic, immobilized proximal tibial metaphyses of female rats. The right hindlimbs of 6-month-old female Sprague-Dawley rats were immobilized by bandaging the right hindlimbs to the abdomen. After 30 days of right hindlimb immobilization, the rats were subcutaneously injected with 200 micrograms hPTH(1-38)/kg/day for 15 days (short-term treatment) or 75 days (longer-term treatment). Static bone histomorphometry was performed on the primary spongiosa, and both static and dynamic histomorphometry were performed on the secondary spongiosa of the right proximal tibial metaphyses. Immobilization for 30 days without treatment decreased trabecular bone area, number, and thickness in both primary and secondary spongiosa, and induced an increase in eroded perimeter and a decrease in tissue referent-bone formation rate in the secondary spongiosa. These changes reached a new steady state thereafter. Treatment with 200 micrograms hPTH(1-38)/kg/day for 15 days, beginning 30 days after immobilization, significantly increased trabecular bone area, thickness, and number in both primary and secondary spongiosa despite continuous immobilization when compared with controls. The short-term PTH treatment (15 days) significantly increased labeling perimeter, mineral apposition rate, and tissue referent-bone formation rate in the secondary spongiosa and stimulated longitudinal bone growth as compared with the controls. Longer PTH treatment (75 days) further increased trabecular bone area, thickness, and number as compared with controls and groups given short-term PTH treatment (15 days). The bone formation indices in the secondary spongiosa of the longer-term treated rats were lower than those of the short-term treated group, but they were still higher than those of controls. Our findings indicate that PTH treatment stimulates cancellous bone formation, and restores and adds extra cancellous bone to the established, disuse-osteopenic proximal tibial metaphysis of female rats with continuously immobilized right hindlimbs. These results suggest that PTH may be useful in treating disuse-induced osteoporosis in humans.

Prostaglandin E2 administration prevents bone loss induced by orchidectomy in rats

The objects of this study were to investigate whether prostaglandin E2 (PGE2) can prevent orchidectomy (ORX)-induced cancellous bone loss in growing male rats, and to determine the differential effects of PGE2 on sham-operated (sham) and ORX male rats. Fourteen-week-old Sprague-Dawley male rats were divided into groups of basal, vehicle-treated sham, PGE2-treated sham, vehicle-treated ORX, and PGE2-treated ORX rats for either 3 or 9 weeks. PGE2 was given at 6 mg/kg body weight daily by subcutaneous injection. Static and dynamic cancellous bone histomorphometry were performed on double-fluorescent labeled undecalcified proximal tibial metaphyseal sections. No effect was observed by ORX on body weight or longitudinal bone growth rate when compared with sham-operated controls. However, androgen deficiency caused significant increases in percent eroded perimeter, mineral apposition rate, and bone turnover (bone-volume-referent-bone formation rate), which resulted in a significant decrease in trabecular bone number, increase in trabecular separation, and a nonsignificant decrease in trabecular bone area by 3 weeks of ORX. After 9 weeks of ORX, trabecular bone area and number were significantly decreased, and trabecular separation, percent eroded perimeter, and the index of bone turnover (bone-volume-referent-bone formation rate) remained significantly increased while the index of bone formation (tissue-volume-referent-bone formation rate) was nonsignificantly decreased when compared with sham controls. When 6 mg PGE2/kg/day was given for 3 and 9 weeks, similar anabolic effects were observed in sham and ORX rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Perspectives: a vital biomechanical model of the endochondral ossification mechanism

BACKGROUND

Mechanical usage effects could explain many features of endochondral ossification and related processes. Mineralization of growth plate cartilage could reduce its mechanical strains enough to make its resorption begin and to guide it in space. By removing most of its mineralized vertical septae, resorption could overload the remainder enough to increase woven bone formation on them and construct the primary spongiosa. After it finishes mineralizing, the primary spongiosa could become stiff enough to begin partial disuse in strain terms, so BMU-based remodeling would begin replacing it with lamellar bone. This would construct the secondary spongiosa. In transferring loads from the growth plate to the cortex, the central metaphyseal spongiosa becomes deloaded. This disuse would make remodeling remove it in the diaphyseal marrow space.

METHODS

The slow growth of epiphyses and apophyses gives their spongiosas more time to adapt to their loads than the metaphyseal spongiosa beneath faster growing growth plates. Compared to metaphyseal trabeculae, this leads to fewer and thicker epiphyseal trabeculae that turn over more slowly and should persist for life because they carry loads for life.

RESULTS

Rapid turnover of metaphyseal cortex in very young subjects could let it strain enough to form woven bone. Increased thickness and slower turnover of this cortex in older subjects could reduce its strains enough to make lamellar bone form there instead. This would compose this cortex mostly of woven bone in the very young and of lamellar bone in adults.

CONCLUSIONS

This model assigns particular importance to the stiffness and strains of tissues (as distinguished from their strength and stresses), to the relative rates of some processes, and to responses of the skeleton's biologic mechanisms to a tissue's typical largest mechanical strains (as distinguished from their stresses).

Perspectives: applications of a biomechanical model of the endochondral ossification mechanism

A biomechanical model of endochondral ossification (Frost and Jee, 1994. Anat. Rec., 240:435-446) can help to explain: (1) some differences in fracture patterns in children and adults, (2) increased fractures during the human adolescent growth spurt, (3) localization of stress fractures and pseudofractures to cortical instead of trabecular bone, (4) increased bone mass in adult-acquired and childhood obesity, (5) subchondral bone densification and osteopenia in some arthroses, (6) why and where mammals lose spongiosa with aging, (7) why, as percents of the original bone stock, metaphyseal trabecular bone losses with aging usually exceed cortical bone losses, (8) why osteochondritis dissecans and aseptic necroses of bone localize in epiphyses instead of metaphyses, (9) some features of growth plate histology in rickets and the chondrodystrophies, (10) why spontaneous fractures in osteoporotic patients affect vertebral more than metaphyseal spongiosa, (11) why osteopenias develop in most chronic, debilitating diseases, and (12) why histomorphometric values can differ in iliac bone biopsies obtained by the "vertical" Jamshidi and "horizontal" Bordier-Meunier techniques.

Relative effectiveness of 239Pu and some other internal emitters for bone cancer induction in beagles

The toxicity ratio (relative effectiveness per gray of average skeletal dose) has been estimated for bone cancer induction in beagles injected as young adults for a number of bone-seeking internal emitters. These experiments yielded calculated toxicity ratios (+/- SD) relative to 226Ra = 1.0 of 239Pu = 16 +/- 5 (single exposure to monomeric Pu) and 32 +/- 10 (continuous exposure from an extraskeletal deposit in the body), 224Ra = 16 +/- 5 (chronic exposure) and approximately 6 +/- 2 (single exposure), 228Th = 8.5 +/- 2.3, 241Am = 6 +/- 0.8, 228Ra = 2.0 +/- 0.5, 249Cf = 6 +/- 3, 252Cf = 4 +/- 2, 90Sr = 1.0 +/- 0.5 (for high doses) and 0.05 +/- 0.03 (for low doses) and 0.01 +/- 0.01 (for extremely low doses). Because no skeletal malignancies were observed among beagles given only 253Es, the toxicity ratio is undefined.

Effects of prostaglandin E2 and risedronate administration on cancellous bone in older female rats

The effects of Prostaglandin E2 (PGE2) and Risedronate (Ris) both separately and in combination (PGE2 + Ris) were studied on the intact aged female rat skeleton to determine whether the combination of PGE2 with an antiresorptive agent is more effective anabolically than PGE2 alone. Nine-month-old Sprague-Dawley rats were injected subcutaneously either with vehicle, 6 mg PGE2/kg per day, 1 or 5 micrograms Ris/kg twice a week, or 6 mg PGE2/kg per day plus 1 or 5 micrograms Ris/kg twice a week (PGE2 + 1 Ris or PGE2 + 5 Ris) for 60 days. After the treatment, we determined the longitudinal bone growth rate, the qualitative appearance of the primary spongiosa (PS), and the static and dynamic bone histomorphometry of the secondary spongiosa (SS) of the proximal tibial metaphysis (PTM) by examining undecalcified longitudinal sections after double-fluorescent labeling. The relative effects of these treatments on longitudinal bone growth were ranked as follows: PGE2 + 5 Ris > PGE2 + 1 Ris = basal > PGE2 > 1 microgram Ris = 5 micrograms Ris = aging. The density of the PS was ranked as follows: PGE2 + 5 Ris > PGE2 + 1 Ris = PGE2 = 5 micrograms Ris = 1 microgram Ris > basal = aging. The increase in density of the PS was the result of stimulated longitudinal growth and the action of bisphosphonate. Bone mass in the SS was ranked as follows: PGE2 + 5 Ris = PGE2 + 1 Ris = PGE2 > 5 micrograms Ris = 1 microgram Ris = aging = basal.(ABSTRACT TRUNCATED AT 250 WORDS)

Skeletal development in newborn and weanling northern elephant seals

The neonatal period in the northern elephant seal (Mirounga angustirostris) differs markedly from that of most mammals. An intense 1-mo nursing period is followed by 2-3 mo during which seal pups consume neither food nor water. Because skeletal development in other species is rapid during this period, we determined the capability of elephant seals to continue skeletal growth under fasting conditions. We analyzed indirect markers of bone turnover [serum osteocalcin and alkaline phosphatase activity and urinary calcium and hydroxyproline (Hyp) excretion] in samples obtained sequentially from live pups throughout the fast. Serum osteocalcin was low at the beginning of the fast, peaked between 17 and 42 days, and then decreased to initial levels after 10 wk. Alkaline phosphatase activity increased linearly through 9 wk of fasting. Urinary calcium was relatively constant through 9 wk but decreased after 10 wk, whereas free and total Hyp decreased linearly. Clearance of 3H-labeled Hyp showed that virtually all (> 99%) free Hyp was oxidized and that only bound Hyp, for which there is no degradative mechanism, was excreted. Kinetics of 45Ca clearance, a direct measurement of mineral turnover, was virtually identical to that for young humans. Histomorphometry of ulnae obtained from pups which died of natural causes (usually trauma inflicted by adult males) indicated active surfaces (osteoid plus eroded) between 30 and 60% of total surface of highly porous bone containing < 60% bone area/tissue area. Thus all indicators of skeletal activity confirmed that young elephant seals continue skeletal development, notwithstanding the prolonged period during which they take in no food or water.

Interferon-gamma causes loss of bone volume in vivo and fails to ameliorate cyclosporin A-induced osteopenia

Interferon-gamma (IFN gamma) in vitro inhibits both bone resorption and bone formation, resulting in a net decrease in bone turnover. In vivo administration of cyclosporin A (CsA) produces accelerated bone remodeling with resultant bone loss. The aim of this study was to investigate whether administration of IFN gamma to rats would favorably modify the high turnover osteopenia caused by CsA. Thirty-six male Sprague-Dawley rats were randomized into 4 equal groups to receive either CsA (15 mg/kg.day) or vehicle by gavage and IFN gamma (10(6) IU/kg.day) or vehicle by ip injection for 8 days. Group 1 received CsA vehicle plus IFN gamma vehicle; group 2 received CsA plus IFN gamma vehicle; group 3 received CsA vehicle plus IFN-gamma; group 4 received CsA plus IFN gamma. Blood was sampled on days 0, 4, and 8 for measurement of ionized calcium (Ca2+), PTH, 1,25-dihydroxyvitamin D, and bone gla protein. Tibiae were removed on day 8 after double tetracycline labeling for histomorphometric analysis. Ca2+ and PTH levels were similar in all groups during the study period. Rats receiving CsA (groups 2 and 4) had elevated levels of 1,25-dihydroxyvitamin D and bone gla protein, whereas rats receiving IFN gamma alone (group 3) had no change in levels of these parameters. Bone histomorphometry revealed that treatment with CsA and/or IFN gamma (groups 2-4) caused an increase in bone resorption surface and a decrease in some parameters of bone formation, resulting in a net loss of bone volume. Thus, IFN gamma failed to influence the osteopenia caused by CsA and on its own had adverse effects on bone in vivo. These results demonstrate that immune-mediating agents have opposing actions in vitro as compared to in vivo.

Mechanical loading modifies ovariectomy-induced cancellous bone loss

The object of this study was to determine the tissue level mechanism in which mechanical loading had an influence on ovariectomy-induced cancellous bone loss. Two experiments were performed: (1) 230 g female rats were divided into basal, age-related controls and right hindlimb immobilized (RHLI) group; (2) 250 g female rats were divided into basal, age-related, ovariectomized (OVX) controls and OVX combined with RHLI. The RHLI model immobilized (IM) or underloaded (UL) the right hindlimb and loaded (L) the left hindlimb compared to the right hindlimb. Both experiments lasted 60 days. Histomorphometric data was gathered from the secondary spongiosa of double fluorescent labeled proximal tibial metaphysis (PTM). The study confirmed that IM or UL induces cancellous bone loss, by decreasing bone formation, and increasing bone resorption and OVX results in cancellous bone loss, a higher bone turnover with bone resorption exceeding bone formation in the PTM. The OVX'd and immobilized (OVX + UL) PTM showed further decreased cancellous bone mass (-48%), decreased number (-43%), and decreased tissue-level bone formation rate (-54%) from that of OVX rats. However, the OVX'd and loaded (OVX + L) PTM partially prevented the OVX-induced cancellous bone loss. The cancellous bone area (+46%), number (+29%), and ratio of node to free end (+70%) were increased and percent eroded perimeter (-44%) and bone resorption rates (-30%) were decreased from OVX rats, but cancellous bone area and number were still significantly lower than those in age-related controls. We found that IM or UL accentuated cancellous bone loss in OVX rats by inhibiting bone formation and that loading partially prevented cancellous bone loss in OVX and RHLI rats by inhibiting bone resorption.

The deleterious effects of long-term cyclosporine A, cyclosporine G, and FK506 on bone mineral metabolism in vivo

Administration of cyclosporine A to male and female rats accelerates bone remodeling and causes bone loss, among other side-effects. The newer immunosuppressant drugs, FK506 and CsG, have been synthesized to counteract the toxic effects of CsA, yet maintain clinical efficacy. We investigated the in vivo effects of long-term administration of these drugs on bone mineral metabolism in the rat. Five groups of Sprague-Dawley rats, 15 per group, were allocated to receive by daily gavage for a period of 28 days: (1) Cs-vehicle; (2) CsA 15 mg/kg b.w.; (3) CsG 15 mg/kg b.w.; (4) FK506 vehicle; (5) FK506 5 mg/kg b.w. Blood was sampled on days 0, 14, and 28 for measurement of ionized calcium (Ca2+), parathyroid hormone (PTH), 1,25-(OH)2-vitamin D, and bone gla protein (BGP). Tibiae were removed on day 28 after double calcein labeling for histomorphometric analysis. Immunosuppressant groups were compared with the respective vehicle groups. Neither CsA or CsG affected the levels of Ca2+ or PTH, whereas by day 28 FK506 caused a decrease in Ca2+ and a corresponding rise in PTH (P < 0.05). The 1,25-(OH)2-vitamin D and BGP levels in both the CsA and CsG groups were increased on days 14 and 28 (P < 0.05), while FK506 had no effect on these serum levels. Tibial bone histomorphometry revealed that all 3 immunosuppressants increased measures of bone formation and bone resorption, accompanied by a significant reduction in percent trabecular area, most marked with FK506. This report demonstrates that all three immunosuppressants have adverse effects on bone--most deleterious with FK506.

Effect of cyclosporin A on bone mineral metabolism in experimental diabetes mellitus in the rat

Cyclosporin A (CsA) is widely used in diabetic transplant patients and early type I diabetes mellitus. Diabetes produces a low-turnover osteopenia, and CsA conversely induces high-turnover osteopenia in rats. We investigated whether CsA would exacerbate diabetic osteopenia. Four groups of 10-week-old male Sprague-Dawley rats (n = 11/group) were studied: On day -6, groups A and C received saline and groups B and D received intravenous streptozotocin (55 mg/kg) to induce diabetes. From day 0, groups A and B received CsA vehicle and C and D received CsA (15 mg/kg) by daily gavage. Rats were bled on days -6, 0, 11, and 22 for serum bone gla protein (BGP), 1,25-(OH)2D, PTH, blood ionized Ca, and blood glucose determinations. Double tetracycline labeling was performed on days 9 and 20 for bone histomorphometry. After sacrifice on day 22, histomorphometric analysis was performed. Serum BGP, 1,25-(OH)2D, and PTH levels were significantly decreased in the diabetic alone (B) and diabetic plus CsA (D) groups and significantly increased in the CsA alone (group C). CsA alone (group C) induced cancellous bone loss by stimulated bone resorption. Cancellous bone loss in the diabetic alone rats (group B) was caused primarily by inhibited bone formation. No differences were found in cancellous bone mass, formation, or resorption parameters between diabetic alone (group B) and CsA-treated diabetic rats (group D). Neither CsA alone (group C) nor diabetic alone (group B) nor their combination affected cortical bone mass. CsA alone (group C) stimulated periosteal bone formation and endocortical bone resorption and inhibited endocortical formation, and diabetic alone (group B) inhibited both periosteal and endocortical bone formation. No parameters of tibial diaphyses in CsA-treated diabetic rats (group D) were different from diabetic alone. Thus the addition of CSA to the diabetic treated rats (group D) could not stimulate remodeling and appeared not to worsen significantly some of the alterations in bone formation and resorption. Possible explanations for this may be that CsA in vivo requires adequate levels of PTH, 1,25-(OH)2D, insulin, and perhaps growth factors to stimulate remodeling. The use of CsA in type I diabetic patients or in organ transplant recipients who remain diabetic after transplantation may in the short term not aggravate existing osteopenia based on these findings.

Distribution of skeletal malignancies in beagles injected with 239Pu citrate

The distribution of skeletal malignancies among our beagles injected with 239Pu as young adults roughly seems to follow the distribution of skeletal mass and skeletal 239Pu. These findings are similar to those we reported previously for a group of dogs given 26Ra. Although there were differences in tumor distribution between the animals given 226Ra and those given 239Pu, most of them were not statistically significant; however, the radium dogs seemed to show a greater sensitivity to bone tumor origin in the tibia, while there may have been a tendency among the plutonium dogs toward increased relative sensitivity in the scapula, lumbar vertebrae, sacrum, and ribs. In contrast, the most common site for the formation of naturally-occurring bone malignancy in the dog is the distal radius. Perhaps there were too few tumors and too few dogs to establish statistical significance. A correlation between tumor location and at least two anatomical-physiological factors in the skeleton indicated that these two factors (site-specific bone turnover rate and percent of red marrow at the site, which is correlated with vascularity) may influence the appearance of malignancies both individually and in combination. Except for the femur, there appeared to be no difference between the relative distribution of skeletal malignancies of low-level (30 Bq-2 Bq kg-1 injected) and high-level (3-122 kBq kg-1) dogs. Distribution of bone tumors between the axial and appendicular skeleton was 50% vs. 50% for 239Pu (42 and 42), but it was 39% axial vs. 61% appendicular (22 and 35, respectively) for dogs given 226Ra. This difference was not significant (p > 0.2).

Prostaglandin E2 adds bone to a cancellous bone site with a closed growth plate and low bone turnover in ovariectomized rats

The objects of this study were to determine the responses of a cancellous bone site with a closed growth plate (the distal tibial metaphysis, DTM) to ovariectomy (OVX) and OVX plus a prostaglandin E2 (PGE2) treatment, and compare the site's response to previous findings reported for another site (the proximal tibial metaphysis, PTM). Thirty-five 3-month-old female Sprague-Dawley rats were divided into five groups: basal, sham-OVX, and OVX + 0, +1, or +6 mg PGE2/kg/d injected subcutaneously for 3 months and given double fluorescent labels before sacrifice. Cancellous bone histomorphometric analyses were performed on 20-microns-thick undecalcified DTM sections. Similar to the PTM, the DTM showed age-related decreases in bone formation and increases in bone resorption, but it differed in that at 3 months post-OVX, there was neither bone loss nor changes in formation endpoints. Giving 1 mg PGE2/kg/d to OVX rats prevented most age-related changes and maintained the bone formation histomorphometry near basal levels. Treating OVX rats with 6 mg PGE2/kg/d prevented age-related bone changes, added extra bone, and improved microanatomical structure by stimulating bone formation without altering bone resorption. Furthermore, after PGE2 administration, the DTM, a cancellous bone site with a closed growth plate, increased bone formation more than did the cancellous bone in the PTM.

Chiral pharmacokinetics of Rac-flurbiprofen and pharmacodynamics of anabolic bone response in the normal rat

The route of administration of the NSAID, flurbiprofen (sq vs. po) resulted in positive and negative results respectively with regard to enhanced cancellous and cortical bone accumulation in the immature rat. This pharmacokinetic study was an effort to understand the pharmacodynamic difference between the two routes of administration observed when the same dose range of drug, given as single daily doses, had been employed in both studies. Conventional chiral pharmacokinetics were evaluated in young rats. A significant difference was observed in the Tmax of the active (S)-enantiomer by both administration routes (sq 4 h and po 1 h). The bioavailability, as evaluated by AUCs favored the sq route as expected. The plasma concentrations over 18 h, at steady state, for one po dose group (0.5 mg/kg/day) fell well within the therapeutic window described by the 0.1 and 0.5 mg/kg sq doses which had demonstrated anabolic bone activity. Oral dosing had exhibited no significant bone activity. We conclude that the pharmacodynamic difference between routes of administration cannot be simply explained on a pharmacokinetic basis. Consequently, experiments detailing the pharmacodynamics and pharmacokinetics of single and multiple dose administration of aryl-propionic acids in normal and osteopenic states need further pharmacologic study.

Hits to bone cell nuclei from nonuniform radioactive labels

The stochastic aspects of alpha-particle traversals through nuclei of bone-lining cells from nonuniform radioactive labels are worked out. Both the residence time of the target and the hit rate are considered random variables. It is shown that with any type of bone remodeling the fraction of cells not hit increases with increasing nonuniformity of the label concentration. Thus, a completely uniform concentration represents the most dangerous situation. A possible negative correlation between residence times and hit rates, observed in some experiments, tends to decrease the probability of alpha-particle hits. As a practical application, the theory is applied to the International Commission on Radiological Protection model of the distribution of 239Pu in the human body. In the case of 50 years of chronic ingestion of 1 annual limit of intake (ALI) per year for class W and chronic inhalation of 1 ALI/year for class Y compounds, more than 19.4 and 8.5% of the nuclei of bone-lining cells are traversed by at least one alpha-particle, respectively.

Application of computer-based histomorphometry to the quantitative analysis of methylprednisolone-treated adjuvant arthritis in rats

Analyses of paw edema and histomorphometry were performed on tibio-talar joints to determine arthritic pathological responses in untreated 28-day adjuvant-induced polyarthritis (AIP) rats, and to determine the drug effect on inhibiting these responses in AIP rats treated with methylprednisolone. Histomorphometric measurements were performed on regions including articular joint space, synovial tissue, articular and epiphyseal cartilage, epiphyseal and metaphyseal bone marrow, and endosteal and periosteal cortical bone surfaces. Analysis of paw edema indicated that paw volume was significantly increased in untreated AIP rats. This increase in paw volume was partially prevented in AIP rats treated with 0.3 mg methylprednisolone/kg per day, and completely prevented in AIP rats treated with the two higher dose levels (1 and 3 mg/kg per day). Histomorphometric analysis of untreated AIP tibio-talar joints showed decreased articular joint space whereas synovial tissue area increased and a minor, but significant, articular cartilage erosion area occurred. Epiphyseal growth cartilage area was decreased. Trabecular bone area in distal tibial epiphyseal and metaphyseal regions was markedly decreased whereas bone marrow area increased involving a large number of macrophages and osteoclasts. Eroded endocortical bone area was increased while cortical bone area decreased. Marked osteophyte proliferation occurred on the periosteal surface. These arthritic pathological changes were inhibited by the treatment of methylprednisolone in a dose-dependent fashion. The animals treated with the highest dose of methylprednisolone complete prevented the development of the AIP-induced pathological changes. These data confirmed qualitative histological evaluation of arthritic changes but did not correlate with the anti-edema effects of methylprednisolone (100% inhibition at 1.0 and 3.0 mg/kg, p.o.). It is suggested that quantitative histomorphometry be used to determine more precisely the AIP rat model and the effects of drugs on different histopathological features in this experimental model of arthritis in preference to paw edema which gives a more limited picture of the arthritic response.

Anabolic responses of an adult cancellous bone site to prostaglandin E2 in the rat

The objects of this study were to determine: (1) the response of a non-growing cancellous bone site to daily prostaglandin E2 (PGE2) administration; and (2) the differences in the effects of daily PGE2 administration in growing (proximal tibial metaphysis, PTM) and non-growing cancellous bone sites (distal tibial metaphysis, DTM). Seven-month-old male Sprague-Dawley rats were given daily subcutaneous injections of 0, 1, 3 and 6 mg PGE2/kg per day for 60, 120 and 180 days. The static and dynamic histomorphometric analyses were performed on double-fluorescent labeled undecalcified distal tibial metaphyses (DTM). No age-related changes were found in static and dynamic histomorphometry of DTM cancellous bone between 7 and 13 months of age. The DTM of 7-month-old (basal controls) rats consisted of a 24.5 +/- 7.6%-metaphyseal cancellous bone mass, and a thick trabeculae (92 +/- 12 micron). It also had a very low tissue-base bone formation rate (3.0 +/- 7.3%/year). Exogenous PGE2 administration produced the following transient changes in a dose-response manner between zero and 60 days: (1) increased trabecular bone mass and improved architecture (increased trabecular bone area, width and number, and decreased trabecular separation); (2) increased trabecular interconnections; (3) increased bone formation parameters; and (4) decreased eroded perimeter. A new steady state with more cancellous bone mass and higher bone turnover was observed from day 60 onward. The elevated bone mass induced by the first 60 days of PGE2 treatment was maintained by another 60 and 120 days with continuous daily PGE2 treatment. When these findings were compared to those previously reported for the PTM, we found that the DTM was much more responsive to PGE2 treatment than the PTM. Percent trabecular bone area and tissue-based bone formation rate increased significantly more in DTM as compared to PTM after the 60 days of 6 mg PGE2 treatment. These observations indicate that a non-growing cancellous bone site is more responsive than growing bone site to long-term daily administration of PGE2.

Prostaglandin E2 increased rat cortical bone mass when administered immediately following ovariectomy

To investigate the effects of ovariectomy and the simultaneous administration of prostaglandin E2 (PGE2) on rat tibial shaft cortical bone histomorphometry, thirty-five 3-month-old female Sprague-Dawley rats were either ovariectomized (OVX), or sham ovariectomy (sham-OVX). The OVX rats were divided into three groups and treated with 0, 1 and 6 mg PGE2/kg/day for 90 days. The double fluorescent labeled undecalcified tibial shaft cross sections (proximal to the tibiofibular junction) of all the subjects were used for histomorphometry analysis. No differences in cross-sectional area and cortical bone area were found between sham-OVX and OVX controls, but OVX increased marrow area, intracortical porosity area and endocortical eroded perimeter. Periosteal and endocortical bone formation rates decreased with aging yet OVX prevented these changes. These OVX-induced increases in marrow area and endocortical eroded perimeter were prevented by 1 mg PGE2/kg/day treatment and added bone to periosteal and endocortical surfaces and to the marrow cavity. At the 6 mg/kg/day dose level, PGE2-treated OVX rats increased total tissue area, cortical bone area, marrow trabecular bone area, minimal cortical width and intracortical porosity area, and decreased marrow area compared to basal, sham-OVX and OVX controls. In addition, periosteal bone formation was elevated in the 6 mg PGE2/kg/day-treated OVX rats compared to OVX controls. Endocortical eroded perimeter increased from basal and sham-OVX control levels, but decreased from OVX control levels in the 6 mg PGE2/kg/day-treated OVX rats. Our study confirmed that ovariectomy does not cause osteopenia in tibial shaft cortical bone in rats, but it does stimulate endocortical bone resorption and enlarges marrow area. The new findings from the present study demonstrate that PGE2 prevents the OVX-induced increases in endocortical bone resorption and marrow area and adds additional bone to periosteal and endocortical surfaces and to marrow cavity to increase total bone mass in the tibial shaft of OVX rats when given immediately following ovariectomy.

S-ketoprofen inhibits tenotomy-induced bone loss and dynamics in weanling rats

The objects of this study were to determine whether S-Ketoprofen, a non-steroidal anti-inflammatory drug (NSAID), can prevent immobilization (tenotomy)-induced bone loss in weanling rats. Forty-five 4-week-old Sprague-Dawley female rats were either sham-operated or subjected to knee tenotomy and treated simultaneously with 0, 0.02, 0.1, 0.5 or 2.5 mg of S-ketoprofen/kg per day for 21 days. We then studied double-fluorescent labeled proximal tibial longitudinal sections and tibial shaft cross sections using static and dynamic histomorphometry. Less cancellous bone mass in proximal tibial metaphyses was found in tenotomized controls than in basal (36%) and sham-operated (54%) controls. This was due to the inhibition of age-related bone gain and induced bone loss due to increased bone resorption and decreased bone formation. S-ketoprofen prevented both the inhibition of age-related bone gain and the stimulation of bone loss at the 2.5 mg/kg per day dose level, while it only prevented bone loss at the 0.5 mg/kg dose levels. In cancellous bone, dynamic histomorphometry showed that S-ketoprofen prevented the tenotomy induced decrease in bone formation and increase in bone resorption. In the tibial shaft, tenotomy inhibited the enlargement of total tissue area by depressing periosteal bone formation, and thus inhibited age-related cortical bone gain. S-ketoprofen treatment did not prevent this change at all dose levels, but reduced marrow cavity area to increase cortical bone area at the 0.1, 0.5 and 2.5 mg/kg per dose levels compared to tenotomy controls. However, the cortical bone area in the 0.1 and 0.5 mg dose-treated tenotomy rats was still lower than in the age-related controls. S-ketoprofen also prevented the increase in endocortical eroded perimeter induced by tenotomy. In summary, tenotomy inhibited age-related bone gain and stimulated bone loss in cancellous bone sites, and only inhibited age-related bone gain in cortical bone sites. S-ketoprofen treatment at the highest dose levels prevented the changes in cancellous bone, and reduced marrow area to increase cortical bone in the tibial shafts.

Prostaglandin E2 restores cancellous bone to immobilized limb and adds bone to overloaded limb in right hindlimb immobilization rats

The purpose of this study was to determine whether prostaglandin E2 (PGE2) can restore cancellous bone mass and architecture to osteopenic, continuously immobilized (IM), proximal tibial metaphysis (PTM) in female rats. The right hindlimb of three and one-half-month-old Sprague-Dawley female rats were immobilized by right hindlimb immobilization (RHLI) in which the right hindlimb was underloaded and the contralateral left limb was overloaded during ambulation. After 4 or 12 weeks of RHLI, the rats were treated with 3 or 6 mg PGE2/kg/day and RHLI for 8 or 16 weeks. Bone histomorphometry was performed on microradiographs of PTM. Immobilization (IM) induced a transient cancellous bone loss and decreased trabecular thickness, number and node density, and increased free end density that established a new steady state after 4 weeks of IM. Three or 6 mg PGE2/kg/d for 8 weeks beginning at 4 or 12 weeks of IM completely restored cancellous bone mass (+127% to +188%) and structure to the age-related control levels in spite of continuous IM. Another 8 weeks of treatment maintained bone mass and architecture at these levels. No differences in cancellous bone mass and architecture were found between the overloaded PTM or RHLI rats and the age-related controls. However, 3 and 6 mg/kg/d of PGE2 treatment started at 4 or 12 weeks for 8 weeks significantly increased cancellous bone mass in the overloaded PTM (+45 to +74% of untreated controls), and another 8 weeks of treatment maintained bone mass at these levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Greater bone formation induction occurred in aged than young cancellous bone sites

We have determined the differences in the effects of continual prostaglandin E2 (PGE2) treatment in aged (non-growing) and young (growing) cancellous bone sites in 7-month-old Sprague-Dawley rats. The sites involved are the aged distal tibial metaphysis (DTM) with a closed epiphysis and the young proximal tibial metaphysis (PTM) with a slow growing, open epiphysis. The study involved rats treated with 0, 1, 3 or 6 mg PGE2/kg/d for 60, 120 and 180 days. Static and dynamic histomorphometry of percent trabecular area, and tissue-referent bone formation rate (BFR/TV) were determined in both DTM and PTM. In pretreatment controls, the secondary spongiosa of the two metaphyses contain the same amount of cancellous bone (11% in DTM vs. 13% in PTM), but markedly less bone formation in DTM (0.6%/y in DTM vs. 41.5%/y in PTM). After 60 days of 6 mg PGE2/kg/d treatment, %Tb.Ar was increased 607% in DTM and 199% in PTM, BFR/TV was increased to nearly 14 fold in DTM and only 5 fold in PTM. These results indicated the aged metaphysis of the DTM was much more responsive to PGE2 treatment than young, growing metaphysis of the PTM. The results of 120 and 180 days treatment did not significantly differ from 60 days treatment in both sites, indicating that the effect of continuous daily PGE2 treatment were in equilibrium after 60 days. We concluded that aged metaphysis was much more responsive to PGE2 treatment than young growing metaphysis.

Maintaining restored bone with bisphosphonate in the ovariectomized rat skeleton: dynamic histomorphometry of changes in bone mass

This experiment contains the crucial data for the Lose, Restore and Maintain (LRM) concept, a practical approach for reversing existing osteoporosis. The LRM concept uses ovariectomy (ox) to lose bone, an anabolic agent to restore bone mass and then switches to an antiresorptive agent to maintain bone mass. We ox'd or sham-ox'd rats for 150 days (Loss Phase), treated them with 6 mg PGE2/kg/d for 75 days to restore lost cancellous bone mass (Restore Phase) and then stopped PGE2 treatment and began treatment with 1 or 5 micrograms/kg Risedronate, a bisphosphonate twice a week for 60 days (Maintain Phase). During the Loss Phase, cancellous bone volumes of the proximal tibial metaphysis (PTM) in the ox'd rat fell to 19% of initial controls. During the Restore Phase, the PTM bone volume in ox'd rats doubled. However, when PGE2 treatment was stopped, the PGE2-induced cancellous bone disappeared. In contrast, 5 micrograms of Risedronate inhibited the bone loss and maintained it at the PGE2 treatment level. The key dynamic histomorphometry value for the restore (R) and maintenance (M) phases was the ratio of bone formation to resorption rates. The ratio was elevated to 5.8 in the R phase and depressed to 0.4 for no and 1 microgram Risedronate treated M phase and to a ratio of near unity of 1.1 for the 5 micrograms Risedronate treatment. These findings indicate that we were successful in maintaining the new PTM bone induced by PGE2 after discontinuing PGE2 by administering enough Risedronate, a resorption inhibitor.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for reduced cancellous bone mass in the spontaneously hypertensive rat

The histomorphometric changes in the proximal tibial metaphysis and epiphyseal growth plate and midtibial shaft of 26-week-old spontaneously hypertensive rats (SHR) compared with those of the corresponding normotensive Wistar-Kyoto (WKY) rats were studied. A decrease in body weight, growth plate thickness, and longitudinal growth rate of the proximal tibial epiphysis, trabecular bone volume, trabecular thickness and number, the number of osteoblasts and osteoprogenitor cells per millimeter square surface of the proximal tibial metaphysis, periosteal and endocortical apposition rate and bone formation rate of the tibial diaphysis were observed in the SHR. Additionally, systolic blood pressure, the number of osteoclasts per millimeter square surface and average number of nuclei per osteoclast of the proximal tibial metaphysis were significantly increased. Thus, osteoclastic activity is dominant over osteoblastic and chondroblastic activity in the SHR that results in a cancellous bone deficit in the skeleton. It will require additional work to ascertain the underlying cause for this condition as several factors in the SHR with a potential for causing this change are present, including elevated parathyroid hormone (PTH), depressed 1,25-(OH)2D3, low calcium absorption, reduced body weight (reduced loading) elevated blood pressure and possibly other direct cell differences in the mutant strain. At present elevated PTH and adaptation to underloading from reduced weight are postulated to be a likely cause, but additional studies are required to test this interpretation.

Statistics of hits to bone cell nuclei

The statistics of hits to the nuclei of bone cells irradiated from alpha sources labeling bone tissue is described. It is shown that the law of remodeling of a bone structural unit (BSU), which describes the distribution of quiescence periods of this unit, affects the statistics of hits. It the irradiation of bone cells occurs during the whole cell cycle, the mean number of hits is independent of the law of remodeling. In this case the variance of hits has the minimum value for constant quiescence periods of BSUs (deterministic remodeling) and the maximum value for exponentially distributed quiescence periods (random remodeling). For the first generation of bone cells, i.e. for the cells which existed at the moment of the uptake of the nuclide, the mean number of hits depends on the law of remodeling. For random remodeling the mean number is equal to the mean value for the complete remodeling cycle. For deterministic remodeling the mean is only half this value. For the first generation of bone cells, changing the law of remodeling from random to deterministic increases the probability of no hits to the nuclei of bone cells. For the same mean value of hits, the difference does not exceed 13.3% of the total number of cells. For the subsequent generations of bone cells, such a change of the law of remodeling decreases the probability of no hits by 20.4%.