Intermittent parathyroid hormone enhances the healing of medication-related osteonecrosis of the jaw lesions in rice rats

Medication-related osteonecrosis of the jaw (MRONJ) is a potentially severe adverse event in patients treated with antiresorptives. Management of MRONJ is challenging, and no non-antibiotic, established medical treatment exists. Intermittent parathyroid hormone (iPTH) has been used off-label to treat MRONJ with favorable results. However, its medical efficacy has rarely been substantiated in clinical or preclinical experiments. Using a validated rice rat, infection-based model of MRONJ, we evaluated the effects of iPTH on established MRONJ. We hypothesize that iPTH contributes to MRONJ resolution by enhancing alveolar bone turnover and healing oral soft tissues. Eighty-four rice rats began a standard rodent chow diet at age 4 weeks to induce localized periodontitis. Rats were simultaneously randomized to receive saline (vehicle, VEH) or zoledronic acid (ZOL, 80 μg/kg IV) every 4 weeks. Oral exams were conducted bi-weekly to assign a gross quadrant grade (GQG, 0-4) to evaluate any lesion at the lingual aspect of the interdental space between maxillary molar (M2) and M3. 14 of 20 VEH-treated rice rats (70%) developed maxillary localized periodontitis with GQG 2-3 after 30 ± 10 weeks of saline. Additionally, 40 of 64 ZOL-treated rice rats with periodontitis developed MRONJ-like lesions after 30 ± 10 weeks of ZOL treatment. Rice rats with localized periodontitis or MRONJ-like lesions were treated with saline or iPTH (40 μg/kg) subcutaneously (SC) 3 times/week For 6 weeks until euthanasia. We found that iPTH -treated ZOL rats had a lower prevalence of MRONJ (p < 0.001), with lower severity extent of oral lesions (p = 0.003) and percentage of empty osteocyte lacunae (p < 0.001). ZOL rats treated with iPTH displayed a higher osteoblast surface (p < 0.001), more osteoblasts (p < 0.001), higher osteoclast surface (p < 0.001) and more osteoclasts (p = 0.002) at alveolar bone surfaces than ZOL/VEH rats. Greater gingival epithelial thickness and epithelial cell proliferation rate was found in the oral mucosa and gingiva of ZOL/PTH rats than in ZOL/VEH rats (p < 0.001). Our data suggest that iPTH is an efficacious non-operative medicinal therapy that accelerates oral healing and enhances the resolution of MRONJ lesions in ZOL-treated rice rats.

Bone architecture, bone material properties, and bone turnover in non-osteoporotic post-menopausal women with fragility fracture

Macro- and microarchitectural, bone material property, dynamic histomorphometric, and bone turnover marker data were studied in normal bone mineral density (BMD) post-menopausal women with fragility fracture. Women with fracture had thinner iliac cortices and more homogeneous bone material properties in cortical bone than age/BMD-matched non-fracture women. Low cortical thickness and bone tissue heterogeneity in normal BMD women are associated with prevalent fragility fracture.

INTRODUCTION

Bone mass (bone mineral density, (BMD)) of the spine and hip is today's best single measurement for evaluating future fragility fracture risk. However, the majority of fragility fractures occur in women with BMD T-score above the WHO osteoporotic BMD threshold of - 2.5, indicating that non-BMD endpoints may play a role in their fragility fractures. We hypothesize that in non-osteoporotic women, bone micoarchitecture, bone material properties, dynamic histomorphometric endpoints, and bone turnover markers are related to fragility fracture.

METHODS

Two groups (N = 60 each) of post-menopausal women with total hip BMD T-score ranging from + 0.3 to -2.49 were recruited: fragility fracture and age/BMD-matched, non-fragility fracture women. Normal (T-score >  - 0.99) and osteopenic (T-score ≤  - 1.0) BMD cohorts were designated within both the fracture and non-fracture groups. Transiliac biopsy specimens were obtained to evaluate dynamic histomorphometric and microarchitectural endpoints and bone material properties by static and dynamic nanoindentation testing. All variables for fracture and non-fracture women within each BMD cohort were compared by the Wilcoxon signed-rank test (P < 0.01).

RESULTS

Compared to non-fracture/normal BMD women, fracture/normal BMD women display lower iliac cortical thickness (- 12%, P = 0.0041) and lower heterogeneity of hardness (- 27%, P = 0.0068), elastic modulus (- 35%, P = 0.0009), and storage modulus (- 23%, P = 0.0054) in the cortical bone tissue, and lower heterogeneity of hardness (- 13%, P = 0.0088) in the trabecular bone tissue. Osteopenic women had no abnormalities related to fracture status.

CONCLUSION

Post-menopausal women with normal BMD and fragility fracture have low cortical thickness and heterogeneity of several bone material properties in cortical and trabecular mineralized bone tissue. These differences may explain a portion of the excess bone fragility in women with normal BMD and fragility fracture.

Biologic and pathologic aspects of osteocytes in the setting of medication-related osteonecrosis of the jaw (MRONJ)

Medication-related osteonecrosis of the jaw (MRONJ) is a potentially severe, debilitating condition affecting patients with cancer and patients with osteoporosis who have been treated with powerful antiresorptives (pARs) or angiogenesis inhibitors (AgIs). Oral risk factors associated with the development of MRONJ include tooth extraction and inflammatory dental disease (e.g., periodontitis, periapical infection). In bone tissues, osteocytes play a bidirectional role in which they not only act as the "receiver" of systemic signals from blood vessels, such as hormones and drugs, or local signals from the mineralized matrix as it is deformed, but they also play a critical role as "transmitter" of signals to the cells that execute bone modeling and remodeling (osteoclasts, osteoblasts and lining cells). When the survival capacity of osteocytes is overwhelmed, they can die. Osteocyte death has been associated with several pathological conditions. Whereas the causes and mechanisms of osteocyte death have been studied in conditions like osteonecrosis of the femoral head (ONFH), few studies of the causes and mechanisms of osteocyte death have been done in MRONJ. The three forms of cell death that affect most of the different cells in the body (apoptosis, autophagy, and necrosis) have been recognized in osteocytes. Notably, necroptosis, a form of regulated cell death with "a necrotic cell death phenotype," has also been identified as a form of cell death in osteocytes under certain pathologic conditions. Improving the understanding of osteocyte death in MRONJ may be critical for preventing disease and developing treatment approaches. In this review, we intend to provide insight into the biology of osteocytes, cell death, in general, and osteocyte death, in particular, and discuss hypothetical mechanisms involved in osteocyte death associated with MRONJ.

Preclinical models of medication-related osteonecrosis of the jaw (MRONJ)

Medication-related osteonecrosis of the jaw (MRONJ) is a potentially severe adverse event affecting patients with cancer and patients with osteoporosis who have been treated with powerful antiresorptives (pARs) or angiogenesis inhibitors (AgIs). pARs, including nitrogen-containing bisphosphonates (N-BPs; e.g., zoledronic acid, alendronate) and anti-RANKL antibodies (e.g., denosumab), are used to manage bone metastases in patients with cancer or to prevent fragility fractures in patients with osteoporosis. Though significant advances have been made in understanding MRONJ, its pathophysiology is still not fully elucidated. Multiple species have been used in preclinical MRONJ research, including the rat, mouse, rice rat, rabbit, dog, sheep, and pig. Animal research has contributed immensely to advancing the MRONJ field, particularly, but not limited to, in developing models and investigating risk factors that were first observed in humans. MRONJ models have been developed using clinically relevant doses of systemic risk factors, like N-BPs, anti-RANKL antibodies, or AgIs. Specific local oral risk factors first noted in humans, including tooth extraction and inflammatory dental disease (e.g., periodontitis, periapical infection, etc.), were then added. Research in rodents, particularly the rat, and, to some extent, the mouse, across multiple laboratories, has contributed to establishing multiple relevant and complementary preclinical models. Models in larger species produced accurate clinical and histopathologic outcomes suggesting a potential role for confirming specific crucial findings from rodent research. We view the current state of animal models for MRONJ as good. The rodent models are now reliable enough to produce large numbers of MRONJ cases that could be applied in experiments testing treatment modalities. The course of MRONJ, including stage 0 MRONJ, is characterized well enough that basic studies of the molecular or enzyme-level findings in different MRONJ stages are possible. This review provides a current overview of the existing models of MRONJ, their more significant features and findings, and important instances of their application in preclinical research.

Preventing or controlling periodontitis reduces the occurrence of osteonecrosis of the jaw (ONJ) in rice rats (Oryzomys palustris)

INTRODUCTION

Osteonecrosis of the jaw (ONJ) is an adverse event that requires association of both systemic risk factors, such as powerful anti-resorptives (pARs; e.g. zoledronic acid [ZOL]), and local oral risk factors (e.g. tooth extraction, periodontitis). Whereas optimal oral health prior to initiate pARs is recognized as critically important for minimizing ONJ risk, the efficacy of preventive/maintenance measures in patients who are taking pARs is understudied. Rice rats fed a standard diet (STD), rich in insoluble fiber, develop localized periodontitis. STD-rats with localized periodontitis treated with ZOL for 18-24 wk develop ONJ. Hence, we hypothesized that controlling/preventing localized periodontitis in the ZOL-treated rats, reduces ONJ occurrence.

METHODS

We used two approaches to attempt reducing periodontitis prevalence: 1) periodontal cleaning (PC); and 2) replacing the STD-diet with a nutritionally-equivalent diet high in soluble fiber (SF). 75 four-week-old male rats were weight-randomized into five groups (n = 15) in a 24-week experiment. Three groups ate the STD-diet and two the high SF-diet. STD-diet groups received intravenous (IV) vehicle (VEH) q4wks (STD + VEH), 80 μg/kg ZOL q4wks IV (STD + ZOL), or ZOL plus PC q2wks (STD + ZOL + PC). The SF-diet groups received VEH (SF + VEH) or ZOL (SF + ZOL). Jaws were processed for histopathology and evaluated for ONJ prevalence and tissue-level periodontitis.

RESULTS

1) 40% of STD + VEH rats developed maxillary localized periodontitis with no ONJ; 2) 50% of STD + ZOL rats developed ONJ; 3) 7% of STD + ZOL + PC rats developed ONJ (p < 0.01 vs. STD + ZOL); and 4) one SF + ZOL rat developed localized periodontitis, and no SF + VEH or SF + ZOL rats developed ONJ (p < 0.001 vs. STD + ZOL).

CONCLUSIONS

1) Periodontal cleaning in ZOL-treated rats decreases localized periodontitis severity and reduces ONJ prevalence; and 2) feeding a SF-diet to ZOL-treated rats reduces both incidence of localized periodontitis and ONJ. Our data indicates strong oral microbial community shifts according to oral health condition and trends in the shifts associated with diet.

Anti-vascular endothelial growth factor antibody monotherapy causes destructive advanced periodontitis in rice rats (Oryzomys palustris)

OBJECTIVE

Angiogenesis inhibitors (AgI) are commonly used in combination chemotherapy protocols to treat cancer, and have been linked to osteonecrosis of the jaw (ONJ). However, it is unknown if AgI therapy alone is sufficient to induce ONJ. We have previously established an ONJ model in rice rats with localized periodontitis that receive zoledronic acid (ZOL). The purpose of this study was to use this model to determine the role of anti-vascular endothelial growth factor A (anti-VEGF) antibody treatment of rice rats with localized maxillary periodontitis. We hypothesized that rice rats with localized maxillary periodontitis given anti-VEGF monotherapy will develop oral lesions that resemble ONJ, defined by exposed, necrotic alveolar bone.

METHODS

At age 4 weeks, 45 male rice rats were randomized into three groups (n = 15): 1) VEH (saline), 2) ZOL (80 μg/kg body weight, intravenously once monthly), and 3) anti-VEGF (5 mg B20-4.1.1/kg body weight, subcutaneously twice weekly). After 24 weeks, rats were euthanized, jaws were excised and a high-resolution photograph of each quadrant was taken to assign a severity grade based on gross appearance. Jaws were then fixed, scanned by MicroCT, decalcified and sectioned for histopathologic and immunohistochemical analyses.

RESULTS

40-80% of the rats in the three groups developed gross oral lesions. 50% of ZOL rats developed ONJ. In contrast, 80% of the anti-VEGF rats developed destructive advanced periodontitis that was characterized by extreme alveolar bone loss and fibrosis. Anti-VEGF rats never developed exposed, necrotic bone. Furthermore, only anti-VEGF rats developed mild to severe mandibular periodontitis. Compared to VEH rats, more T-cells were found in periodontal lesions of anti-VEGF rats and more cells of the monocyte lineage were found in ONJ lesions of ZOL rats.

CONCLUSIONS

Anti-VEGF monotherapy administered to a validated rodent model of ONJ caused a destructive advanced form of periodontitis that differed significantly from ONJ.

Inhibition of vascular endothelial growth factor in young adult mice causes low bone blood flow and bone strength with no effect on bone mass in trabecular regions

Objective

To determine the effect of an antibody to vascular endothelial growth factor (VEGF) on bone blood flow, bone strength, and bone mass in the young adult mouse.

Methods

Ten-week-old male BALB/cJ mice were body weight-randomized into either a rodent anti-VEGF monoclonal antibody (anti-VEGF, B20-4.1.1; 5 mg/kg 2×/wk.; n = 12) group or a vehicle (VEH; n = 12) group. After 42 days, mice were evaluated for bone blood flow at the distal femur by ¹⁸F-NaF-PET/CT and then necropsied. Samples from trabecular and cortical bone regions were evaluated for bone strength by mechanical testing, bone mass by peripheral quantitative computed tomography (pQCT), and micoarchitecture (MicroCT). Hydration of the whole femur was studied by proton nuclear magnetic resonance relaxometry (¹H NMR).

Results

Distal femur blood flow was 43% lower in anti-VEGF mice than in VEH mice (p = 0.009). Ultimate load in the lumbar vertebral body was 25% lower in anti-VEGF than in VEH mice (p = 0.013). Bone mineral density (BMD) in the trabecular region of the proximal humeral metaphysis by pQCT, and bone volume fraction and volumetric BMD by MicroCT were the same in the two groups. Volume fraction of bound water (BW) of the whole femur was 14% lower in anti-VEGF than in VEH mice (p = 0.003). Finally, BW, but not cortical tissue mineral density, helped section modulus explain the variance in the ultimate moment experienced by the femur in three-point bending.

Conclusion

Anti-VEGF caused low bone blood flow and bone strength in trabecular bone regions without influencing BMD and microarchitecture. Low bone strength was also associated with low bone hydration. These data suggest that bone blood flow is a novel bone property that affects bone quality.

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An antibody to vascular endothelial growth factor (anti-VEGF) caused low bone blood flow in a trabecular bone rich region.

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Anti-VEGF did not affect trabecular bone region and bone hydration of the whole femur were also low, trabecular bone mass was not affected by anti-VEGF.

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Bone blood flow may be a bone property that affects bone quality through bone hydration.

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Anti-VEGF caused low trabecular bone strength in the vertebral body and low bone hydration of the whole femur.

Zoledronic acid increases the prevalence of medication-related osteonecrosis of the jaw in a dose dependent manner in rice rats (Oryzomys palustris) with localized periodontitis

OBJECTIVE

Investigate role of dose/duration of zoledronic acid (ZOL), a powerful anti-resorptive (pAR), on prevalence of medication-related osteonecrosis of the jaw (MRONJ) in rice rats (Oryzomys palustris), a species with natural susceptibility to food impaction-induced localized periodontitis (FILP). We hypothesize that ZOL induces MRONJ lesions in rice rats with FILP, and that the prevalence of MRONJ rises with increasing dose and duration of ZOL treatment.

METHODS

We performed a toxicology experiment with clinically-relevant doses of ZOL in female rats (N=230) fed standard (STD) rodent chow. At age 4weeks (baseline), 12 rats were necropsied. The rest were randomized into five groups that began to receive 0, 8, 20, 50 or 125μg/kg ZOL IV/q 4weeks. After 12, 18, 24 and 30weeks, subgroups (N=9-16) from each of the dose groups were necropsied. High-resolution macroscopic photos of all jaw quadrants were given a gross quadrant grade (GQG) (0-4 or MRONJ) that classified FILP lesion severity and determined presence of gross MRONJ. Quadrants with GQG≥1 were examined histopathologically. Logistic regression analysis (ZOL dose/duration) of MRONJ prevalence was completed.

RESULTS

We found: 1) 75% of 0μg/kg ZOL rats developed FILP lesions; 2) baseline rats and rats treated with 0μg/kg ZOL had no MRONJ; 3) 29 gross MRONJ cases were identified; 4) all gross MRONJ cases were confirmed histopathologically by the observation of exposed necrotic bone, and 53 new cases were discovered (total=82); 5) ZOL dose (P<0.001), but not duration (P=0.326), was a significant predictor of MRONJ prevalence; 6) 13% prevalence of gross MRONJ among all rats, with 22% prevalence among rats exposed to ZOL oncologic doses (20-125μg/kg); 7) 38% prevalence of histopathologic MRONJ among all rats, with 73% prevalence among rats exposed to ZOL oncologic doses.

CONCLUSIONS

This is the first experiment to show a dose response relationship between clinically relevant doses of ZOL and MRONJ prevalence.

Effect of Macroanatomic Bone Type and Estrogen Loss on Osteocyte Lacunar Properties in Healthy Adult Women

This is the first study to examine clinical human bone specimens by three-dimensional imaging to characterize osteocyte lacunar properties as a function of macroanatomic bone type and estrogen loss. We applied laboratory-based instrumentation [3D X-ray microscope (3DXRM), MicroXCT-200; Carl Zeiss/Xradia, Inc.] that reaches the same resolution as synchrotron microscopy. We used serial transiliac bone biopsy specimens to examine the effect of macroanatomic bone type and estrogen status on osteocyte lacunar properties. These properties include lacunar size (volume, axes lengths of the ellipsoidal lacunar voids), distribution (density, average near-neighbor lacunar distance), and shape factors (sphericity ratio, average eigenvalues, degree of equancy, elongation, and flatness) in both cortical and trabecular bone tissue. The lacunar properties (volume, surface area, density, near-neighbor distance, etc.) and the shape factors (E1, L1, L2, degree of equancy, degree of elongation) were different between cortical and trabecular bone regardless of estrogen status. In cortical bone and trabecular nodes, the lacunar void volume and surface area were either smaller or tended to be smaller in postmenopausal as compared to premenopausal women. The void volume-to-bone volume ratio of cortical bone showed declining trends with estrogen loss. While there were differences between trabecular and cortical bone tissue, the lacunar void sphericity ratio for trabecular struts shows decreasing trends in postmenopausal women. These data suggest that using 3DXRM can provide new insight into osteocyte lacunar properties in transiliac bone biopsies from patients with various skeletal disease/conditions and pharmaceutical treatments.

Age-related periodontitis and alveolar bone loss in rice rats

OBJECTIVE

To characterize in rice rats: (a) periodontitis (PD) progress with feeding of standard laboratory rat chow (STD) during ages 4-80 weeks; and (b) PD progress with feeding of a high sucrose-casein (H-SC) diet during young adulthood.

METHODS

One group (N=12) was euthanized at age 4 weeks (Baseline). Four groups (N=8-16) consumed a STD diet from baseline and were necropsied at ages 22, 30, 52, and 80 weeks. Three groups (N=10-16) consumed an H-SC diet from baseline. Two were necropsied at ages 22 and 30 weeks, respectively. The third switched to the STD diet at age 22 weeks and was necropsied at age 30 weeks. All mandibles/maxillae were assessed by histometry for degree of periodontal inflammation (PD Score), alveolar crest height (ACH, mm), and horizontal alveolar bone height (hABH, mm²).

RESULTS

In STD diet rats aged ≥30 weeks, all endpoints were worse (P<0.05) than at Baseline. In H-SC diet rats aged ≥22 weeks, all endpoints were worse than at Baseline (P<0.05). At age 22 weeks, all endpoints were worse in the H-SC group than in the STD group (P<0.05). By age 30 weeks, the STD and H-SC groups did not differ.

CONCLUSIONS

1) STD diet fed rice rats develop moderate/severe PD by age 30 weeks; 2) an H-SC diet accelerates moderate/severe PD development; and 3) switching to a STD diet does not halt/reverse PD that was accelerated by an H-SC diet. These data further clarify use of the rice rat as a PD model.

Bone loss in the oestrogen-depleted rat is not exacerbated by sitagliptin, either alone or in combination with a thiazolidinedione

Antihyperglycaemic therapy on bone was evaluated in the ovariectomized (OVX), non-diabetic adult rat. Animals were treated daily for 12 weeks with various doses of sitagliptin, pioglitazone, rosiglitazone, combinations of sitagliptin with pioglitazone or vehicle alone. Sitagliptin target engagement was confirmed by assessing inhibition of plasma dipeptidyl peptidase-4 (DPP-4) and oral glucose tolerance. Parameters related to bone health were evaluated in femur and vertebrae by dual-energy X-ray absorptiometry and histomorphometry. Bone mineral density (BMD) generally did not differ significantly between OVX-sitagliptin-treated animals and OVX-vehicle controls. In lumbar vertebrae, however, there was significantly less BMD loss with increasing sitagliptin dose. Thiazolidinedione (TZD) treatment generally resulted in lower BMD; OVX-TZD-treated (but not OVX-sitagliptin-treated) animals also had lessened cortical thickness in central femur and profoundly greater bone marrow adiposity in lumbar vertebrae. These findings support prior findings with TZDs and suggest a neutral or beneficial impact of DPP-4 inhibition on bone health.

Enhanced alveolar bone loss in a model of non-invasive periodontitis in rice rats

OBJECTIVE

The rice rat (Oryzomys palustris) develops periodontitis-like lesions when fed a diet rich in sucrose and casein (H-SC). We aimed to establish whether this model can accurately mimic the development of human periodontitis.

MATERIALS AND METHODS

For this purpose, 28-day-old rice rats (15/group) were assigned to standard (STD) or H-SC diets and sacrificed after 6, 12, and 18 weeks. Jaws were processed for morphometric, histometric, histologic, histomorphometric, and micro-CT analyses.

RESULTS

We found a progressive increase in horizontal alveolar bone loss (ABL) with age in maxillae of rats fed the STD diet as determined by morphometry. The H-SC diet exacerbated horizontal ABL at the palatal surface at 12 and 18 weeks. Furthermore, increased vertical ABL was detected in mandibles and maxillae of rats fed the H-SC diet for 12 and/or 18 weeks by histometry and micro-CT. Remarkably, the H-SC diet significantly increased bone remodeling at the interproximal alveolar bone of mandibles from rats fed for 6 weeks, but not in those fed for longer periods.

CONCLUSIONS

These findings indicate that the H-SC diet induced a transient increase in alveolar bone remodeling, which is followed by ABL characteristic of moderate periodontitis.

Issues in modern bone histomorphometry

This review reports on proceedings of a bone histomorphometry session conducted at the Fortieth International IBMS Sun Valley Skeletal Tissue Biology Workshop held on August 1, 2010. The session was prompted by recent technical problems encountered in conducting histomorphometry on bone biopsies from humans and animals treated with anti-remodeling agents such as bisphosphonates and RANKL antibodies. These agents reduce remodeling substantially, and thus cause problems in calculating bone remodeling dynamics using in vivo fluorochrome labeling. The tissue specimens often contain few or no fluorochrome labels, and thus create statistical and other problems in analyzing variables such as mineral apposition rates, mineralizing surface and bone formation rates. The conference attendees discussed these problems and their resolutions, and the proceedings reported here summarize their discussions and recommendations.

Maintenance of cancellous bone in ovariectomized, human parathyroid hormone [hPTH(1-84)]-treated rats by estrogen, risedronate, or reduced hPTH

This study compares effects of maintenance doses of human parathyroid hormone [hPTH(1-84)], 17beta-estradiol (E2), and risedronate on distal femur bone mineral density and proximal tibia cancellous bone histomorphometry in ovariectomized (ovx), osteopenic rats previously administered a higher dose of hPTH. Nine groups (n = 8) of 3.5-month-old ovx or intact Sprague-Dawley rats were left untreated for 11 weeks to allow for the development of cancellous osteopenia in the ovx groups. Next, the ovx rats received subcutaneous injections of hPTH (75 microg/kg per day, three times per week) or vehicle for 12 weeks. Treatments were then changed to E2 (10 microg/kg per day, two times per week), risedronate (Ris; 3 microg/kg per day, three times per week), low-dose hPTH(1-84) (LowPTH; 25 microg/kg per day, three times per week), or vehicle, and administered for 36 weeks. The intact control group remained untreated for the duration of study. Femora and tibiae were collected at weeks -11 (baseline); 0 (ovx effect); 12 (hPTH effect), and 24, 36, and 48 (maintenance effects). Endpoints evaluated included distal femur bone mineral density (BMD) and proximal tibia cancellous bone volume (BV/TV), osteoclast surface (Oc.S), mineralizing surface (MS), mineral apposition rate (MAR), and bone formation rate (BFR). Ovariectomy had a negative effect on distal femur BMD and proximal tibia BV/TV. Treatment of ovx rats with hPTH for 12 weeks resulted in higher BMD in comparison to intact controls, and higher cancellous BV/TV in comparison to ovx controls. Discontinuation of hPTH resulted in loss of gained BMD within 24 weeks and loss of gained BV/TV within 12 weeks. Treatment of ovx rats with hPTH for 12 weeks followed by E2 treatment left BMD and BV/TV similar to vehicle-treated ovx rats by week 48 (36 weeks after commencement of the E2 maintenance treatment). Maintenance treatment with risedronate resulted in BMD and BV/TV similar to that of intact controls. Maintenance treatment with low-dose hPTH resulted in greater BMD and similar BV/TV in comparison to intact controls. MS and BFR were highest after low-dose hPTH administration. MS and BFR were lowest after E2 or risedronate, whereas Oc.S was lowest after risedronate administration. Thus, in osteopenic rats, the increment in distal femur BMD and proximal tibia BV/TV gained by 12 weeks of hPTH treatment was lost within 24 and 12 weeks of treatment termination, respectively. Low-dose hPTH maintained BMD and BV/TV after hPTH treatment by stimulating bone formation, whereas risedronate maintained BMD and BV/TV by reducing bone resorption. E2 in a maintenance dose failed to maintain BMD and BV/TV after withdrawal of hPTH treatment.

Maintenance of cortical bone in human parathyroid hormone(1-84)-treated ovariectomized rats

The purpose of this cross-sectional study was to evaluate the effects of human parathyroid hormone(1-84) (hPTH) followed by maintenance treatment with 17beta-estradiol (E(2)), risedronate (Ris), or a reduced dose of hPTH (LowPTH) on cortical bone in the ovariectomized (ovx) rat. Eight groups of ovx and one group of intact female rats (3.5 months) were left untreated for 11 weeks. For the following 12 weeks, four groups received subcutaneous injections of hPTH (75 microg/kg per day on 3 days/week) and four groups received vehicle. Treatments were then changed to E(2) (10 microg/kg per day on 2 days/week), Ris (3 microg/kg per day on 3 days/week), LowPTH (25 microg/kg per day on 3 days/week), or vehicle. Bone tissue was collected at weeks -11 (baseline), 0 (ovx effect), 12 (hPTH effect), 24, 36, and 48 (maintenance effect). Bone mineral density (BMD) and bone mineral content (BMC) of the diaphyseal femur and total cross-sectional area (Tt.Ar), marrow area (Ma.Ar), cortical area (Ct.Ar), and periosteal and endocortical bone formation of the tibia were measured. Ovariectomy resulted in lower BMD (weeks 0-48), unaffected BMC, and greater Tt.Ar (weeks 12 and 36), Ma.Ar (week 48), and Ct.Ar (weeks 0 and 12) compared with intact rats. Endocortical and periosteal bone formation were greater in the ovx than in the intact rats up to 23 weeks postovariectomy. Treatment of ovx rats with hPTH for 12 weeks resulted in greater cortical BMD, BMC, and endocortical bone formation than in intact or ovx controls. In ovx rats pretreated with hPTH and then treated with Ris for 36 weeks, BMD and BMC were greater and Ma.Ar was smaller than in ovx controls. In ovx rats pretreated with hPTH and then treated with LowPTH, BMD, BMC, Ct.Ar, and endocortical bone formation were greater and Ma.Ar was smaller than in ovx controls. Treatment of hPTH-pretreated rats with E(2) for 36 weeks did not affect cortical BMD, BMC, and Ct.Ar, although periosteal bone formation was lower in the E(2) group compared with the ovx group. Thus, in ovariectomized rats, cortical bone gained by 12 weeks of hPTH treatment was maintained for up to 36 weeks by treatment with risedronate or low-dose hPTH, but not with 17beta-estradiol.

No effect of verapamil on the local bone response to in vivo mechanical loading

Verapamil, a calcium channel blocker, alters the intracellular calcium concentration in bone cells in vitro, while mechanical loading stimulates calcium channels. The purpose of this study was to examine the effect of systemic verapamil treatment on the bone response to in vivo external mechanical loading. Female rats (age 5-6 months) were divided into six groups. Half were verapamil treated (0.75 mg/ml drinking water) for 12 weeks. After 8 weeks of treatment, the right tibia was loaded by a four-point bending device. In one set of verapamil and control groups, the right tibia was loaded at 31.8 +/- 0.2 N (36 cycles, 2 Hz, 3 d/wk) for four weeks. A second set was loaded at 40.1 +/- 0.3 N and the third set remained nonloaded. Tibial cortical bone formation and femur bone mineral density (BMD) were evaluated. With loading, bone formation was similarly elevated in loaded tibia of verapamil and control rats (P < 0.003). However, periosteal bone formation (P < 0.001) in the nonloaded tibia, and femoral diaphysis BMD (P < 0.04) were greater in verapamil rats than in controls. We conclude that verapamil, in the dose given, does not interfere with mechanical loading (30, 40 N) at the loaded site and that the voltage-dependent calcium channels, blocked by verapamil, are not significantly involved in the local bone response to increased strain in female rats. However, verapamil increased bone formation and BMD at nonloaded sites of loaded rats. Previously unknown systemic or regional factors associated with loading may explain the potential mechanisms for this interaction and need further investigation.

Effect of parathyroid hormone (hPTH[1-84]) treatment on bone mass and strength in ovariectomized rats

Skeletal fragility in osteoporotic patients is a prominent underlying cause of low-trauma fractures of most bone sites in humans. Clinical research is now focused on developing treatment strategies, including anabolic agents such as parathyroid hormone (PTH), to recover osteoporosis-related bone loss. Female Sprague-Dawley rats (4.5 mo old) were allowed to become osteopenic for 10 wk postovariectomy. Eight rats were killed at the time of ovariectomy (-10 wk) as a baseline control; sham and ovariectomized (OVX) groups were killed at wk 0. Eight rats per group (sham, OVX + vehicle, OVX + hPTH [5 d/wk], and OVX + hPTH [3 d/wk]) were killed after 4, 8, 14, and 20 wk of treatment with 50 microg/kg of human parathyroid hormone (hPTH[1-84]). Bone mineral content and density were measured only in the vertebral body. Bone strength was evaluated in the vertebral body, femoral diaphysis, femoral neck, and distal femur. Significant, lasting osteopenia developed in the vertebral body of OVX rats by 10 wk postovariectomy. Bone mineral density of the vertebral body partially recovered by 8 wk and fully recovered to that seen in sham animals only by 20 wk posttreatment with either a 5 or 3 d/wk dosing schedule of PTH[1-84]. Therefore, hPTH[1-84] (50 microg/kg) given either 3 or 5 d/wk fully restores vertebral and femoral bone strength in osteopenic OVX rats.

Genetic variations in bone density, histomorphometry, and strength in mice

The purpose of this study was to assess breed-related differences in bone histomorphometry, bone biomechanics, and serum biochemistry in three mouse breeds shown to differ in bone mineral density (BMD) (as measured by DXA) and bone mineral content (BMC). Femurs, tibiae, and sera were collected from 16-week-old C3H/HeJ C3H, C57BL/6J BL6, and DBA/2J DBAmice (n = 12/breed). Data collected included BMC and BMD (femora), histomorphometry of cancellous (distal femur) and cortical bone (diaphyseal tibiae and femora), bone strength (femora), and serum alkaline phosphatase (ALP). Consistent with previous reports, BMC and BMD were higher in C3H than in BL6 or DBA mice. The higher BMD in the C3H breed was associated with greater cancellous bone volume, cortical bone area, periosteal bone formation rate, biomechanical strength, and serum ALP. However, mid-diaphyseal total femoral and tibial cross-sectional area and moment of inertia were greatest in BL6, intermediate in C3H, and lowest in DBA mice. The specific distribution of cortical bone in C3H, BL6, DBA mice represents a difference in adaptive response to similar mechanical loads in these breeds. This difference in adaptive response may be intrinsic to the adaptive mechanism, or may be intrinsic to the bone tissue material properties. In either case, the bone-adaptive response to ordinary mechanical loads in the BL6 mice yields bones of lower mechanical efficiency (less stiffness per unit mass of bone tissue) and does not adapt as well as that of the C3H mice where the final product is a bone with greater resistance to bending under load. We suggest that the size, shape, and BMD of the bone are a result of breed-specific genetically regulated cellular mechanisms. Compared with the C3H mice, the lower BMD in BL6 mice is associated with long bones that are weaker because the larger cross-sectional area fails to compensate completely for their lower BMD and BMC.

Bone response to in vivo mechanical loading in C3H/HeJ mice

Bone, being sensitive to mechanical stimulus, adapts to mechanical loads in response to bending or deformation. Although the signal/receptor mechanism for bone adaptation to deformation is still under investigation, the mechanical signal is related to the amount of bone deformation or strain. Adaptation to changes in physical activity depends on both the magnitude of increase in strain above average daily levels for maintaining current bone density and the Minimum Effective Strain (MES) for initiating adaptive bone formation. Given the variation of peak bone density that exists in any human population, it is likely that variation in levels for MES is, to a considerable degree, inherited and varies among animal species and breeds. This study showed a dose-related periosteal response to loading in C3H/HeJ mice. The extent of active formation surface, the rate of periosteal bone formation, and area of bone formation increased with increasing peak periosteal strain. In these mice, the loaded tibia consistently showed lower endocortical formation surface and mineral apposition rate than the nonloaded bones at every load level. Although periosteal expansion is the most efficient means of increasing moment of inertia in adaptation to bending, a dose response increase in endocortical formation would have been predicted. Our characterization of the mouse bone formation response to increasing bending loads will be useful in the design of experiments to study the tibial adaptive response to known loads in different mouse breeds.

On the mechanism of cancellous bone preservation in postmenopausal women with mild primary hyperparathyroidism

Several studies have demonstrated that cancellous bone mass and architecture are preserved in postmenopausal women with primary hyperparathyroidism (PHPT). To investigate the mechanism(s) that could account for this observation, we analyzed features of bone formation in 19 postmenopausal women with PHPT by bone histomorphometry. The results were compared with those from a comparable group of 34 healthy, postmenopausal women. Patients with PHPT were similar to control subjects in cancellous bone area as well as in trabecular width, separation, and number. However, in PHPT, elevations were observed in indexes of bone turnover, such as eroded surface, osteoid surface, mineralizing surface, bone formation rate at the tissue level, and activation frequency. At the level of the bone-remodeling unit, women with PHPT had significantly higher values for the wall width of trabecular bone packets (40.26 +/- 0.36 vs. 34.58 +/- 0.45 mm), the adjusted apposition rate (0.40 +/- 0.04 vs. 0.29 +/- 0.03 mm/day), and the active formation period (67.8 +/- 5.1 vs. 57.3 +/- 2.3 days). These findings are consistent with a stimulatory action of elevated PTH levels on the duration of the active bone formation phase in individual remodeling units and may account at least in part for the preservation of cancellous bone in postmenopausal women with mild PHPT.

Early estrogen replacement therapy reverses the rapid loss of trabecular bone volume and prevents further deterioration of connectivity in the rat

To evaluate the ability of estrogen replacement therapy (ERT) to prevent changes in trabecular bone volume (BV/TV) and connectivity beginning either at ovariectomy (OVX) or 5-13 days after OVX in adult female rats, the right proximal tibial was examined by three-dimensional X-ray tomographic microscopy (XTM) in vivo. Animals had XTM scans of the right tibia and then were randomized into six groups (n = 9). Groups 2-6 had bilateral (OVX), while group 1 was sham-ovariectomized (OVXd) on day 0. Animals were treated with vehicle (groups 1 and 2) or 17beta-estradiol therapy (ERT) at 10 microg/kg three times per week starting at days 0, 5, 8, and 13 post-OVX (groups 3, 4, 5, and 6), until day 50 when they were rescanned by XTM and sacrificed. Trabecular bone structural variables were calculated from XTM data (BV/TVx and beta1/BV/TVx) and standard histomorphometry. Trabecular bone volume (BV/TVx) and the trabecular connections per cubic millimeter of trabecular bone (beta1/BV/TVx) were maintained in both sham-OVXd animals and OVX animals given ERT from the time of OVX. However, OVX + vehicle-treated animals lost 54% BV/TVx and 46% beta1/BV/TVx (p < 0. 01 from day 0). BV/TVx and beta1/BV/TVx decreased rapidly post-OVX to -22% and -25% at day 13 (p < 0.01 from day 0). ERT initiated at day 5, 8, and 13 post-OVX restored BV/TVx to baseline values at day 50 by modestly increasing trabecular plate thickness; however, beta1/BV/TVx was reduced in all OVX groups when compared with their baseline values. ERT also caused a significant reduction in bone turnover compared with OVX + vehicle; however, resorption was suppressed more than formation. These results demonstrate that ERT can restore the lost trabecular bone, but not trabecular connectivity, that occurs soon after OVX by allowing bone formation to continue in previously activated bone remodeling units while suppressing the production of new remodeling units. This may be the mechanism by which prompt intervention with estrogen and other antiresorptive agents can restore bone mass that has been lost from the increase in remodeling space, and thereby reduce the risk of osteoporotic fractures in postmenopausal women.

Bone response to in vivo mechanical loading in two breeds of mice

We investigated the bone response to external loading in C57BL/6J and C3H/HeJ mice, both breeds with low and high bone density, respectively. An in vivo tibial four-point bending device previously used for application of measured external loads in rats was adapted for mice. It delivered a uniform medio-lateral bending moment to the region of the tibia located 1-5.5 mm proximal to the tibio-fibula junction. The right legs of six C57BL/6J [low bone density (LBD)] and C3H/HeJ [high bone density (HBD)] mice were externally loaded in the device for 36 cycles/day at 2 Hz, 6 days/week for 2 weeks at 9.3 +/- 0.9 N force, inducing estimated lateral periosteal surface compressive strains of 5121 +/- 1128 mu epsilon in C3H/HeJ (HBD) mice (n = 6), significantly higher than the estimated 3988 +/- 820 mu epsilon in C57BL/6J mice (n = 6) (mean +/- SD). In addition, C3H/HeJ HBD mice (n = 11) were externally sham (pad pressure or no bending) loaded in the device for 36 cycles/day at 2 Hz, 3 days/week for 3 weeks at 9.3 +/- 0.9 N force. Calcein injections for bone labeling were given at the 10th and 3rd days before sacrifice. At the end of the experiment, all mice were killed and both tibiae were removed, fixed, embedded, and cross-sectioned through the loaded region. Both tibiae were measured for marrow area (Ma.Ar), cortical area (Ct.Ar), total area (Tt.Ar), cross-sectional moment of inertia (CSMI), and periosteal and endocortical woven bone surface (Wo.B/BS), single-labeled surface (sLS), double-labeled surface (dLS), and total formation surface (FS/BS). Differences in all variables due to breed and loading (both bending and sham-bending) were tested by two-way analysis of variance (ANOVA) (P < 0.05). Ma.Ar, Tt.Ar, and CSMI were greater in C57BL/6J (LBD) than in C3H/HeJ (HBD) mice. Periosteal and endocortical woven bone and formation surface were increased significantly more by loading (bending) in C57BL/6J than in C3H/HeJ mice. Periosteal woven bone response due to sham-bending or sham-loading was significantly lower than due to bending loads in the C3H/HeJ mice. We conclude that the bone response to external loading is greater in LBD mice than in HBD mice. The high bone density of C3H/HeJ (HBD) mice is related to breed-specific factors other than the response to loading.

Time course of osteoblast appearance after in vivo mechanical loading

The time course of the bone cellular response to mechanical loading is important in the design of optimal exercise prescriptions. This study examined the time course of periosteal cellular changes in the rat tibia following a single exposure of mechanical loading in four-point bending. The right tibiae of adult female Sprague Dawley rats (n = 48, 346 +/- 29 g) were loaded at 40 N (2000 mu epsilon) for 36 cycles at 2 Hz. Right loaded (L) and left nonloaded (NL) tibiae were collected on days 1, 2, 3, 4, 6, and 9 after loading. Cross sections from the loaded region were examined for periosteal differences in bone lining cell surface length, osteoblast surface length, and both alkaline phosphatase-positive cell surface length and width in the cellular layer. A single loading session increased osteoblast surface length as early as day 2, with a peak in expression on day 3. Nine days after a single loading session osteoblast surface length was not different from nonloaded control levels. Alkaline phosphatase width in the cellular periosteum was elevated by day 2 and remained elevated through day 9. This study shows the transient increase in osteoblast surface following a single loading session. It provides fundamental information regarding the timing of osteoblast appearance and the longevity of the response following mechanical stimulation.

Short-term effects of nicotine on bone and calciotropic hormones in adult female rats

This study assessed the effects of two months nicotine treatment on bone formation and resorption end-points in adult, female rats. In addition, the concentrations of calciotropic hormones which included parathyroid hormone, calcitonin, 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D in rats (7 months old) were determined. All animals received either saline (n = 7/group), nicotine (3.0 mg/kg/day) (n = 7/group) or nicotine (4.5 mg/kg/day) (n = 7/group) via subcutaneous implantation of osmotic minipumps containing either saline or nicotine for a period of two months. Serum, right tibia, left femur and lumbar vertebra (3-5) were collected for determination of hormonal concentrations as well as various parameters, including histomorphometry, bone mineral density, bone mineral content and vertebral strength. Although nicotine-treated rats showed a lower level of 25-hydroxyvitamin D [54.4 +/- 3.1 ng/ml for the 3.0 mg/kg/day and 55.8 +/- 2.8 for the 4.5 mg/kg/day group] (mean +/- S.E.M.) as compared to controls (74.8 +/- 2.8 ng/ml) (P < 0.01, Newman-Keuls test), no significant difference could be detected for the levels of the remaining hormones. Similarly, no statistical differences were detected on histomorphometric end-points, bone mineral density, bone mineral content and vertebral strength of rats. We conclude that, in spite of lowering serum 25-hydroxyvitamin D by about 30%, nicotine administration of two months duration does not alter bone mass, strength or formation and resorption end-points.

Acute changes in trabecular bone connectivity and osteoclast activity in the ovariectomized rat in vivo

Estrogen deficiency results in a loss of trabecular bone mass and structure that leads to an increased incidence of osteoporotic fractures. The purpose of this study was to determine the time course for trabecular structure deterioration and changes in bone turnover just after ovariectomy in the rat. Six-month-old female virgin Sprague-Dawley rats had their right proximal tibia scanned by X-ray tomographic microscopy (XTM) at baseline (day 0). Animals were then randomized into two groups, and in each group 9 were sham-operated and 11 were ovariectomized and had repeat XTM scans on days 5, 13, 29, and 42 postovariectomy in group 1 and on days 8, 13, 33, and 50 postovariectomy in group 2. Urine was collected for deoxypyridinoline (DPD) cross-link measurements 24 h before each XTM scan and analyzed by ELISA. Trabecular bone structural variables and bone turnover endpoints were calculated from XTM data and standard histomorphometry. Trabecular connectivity decreased 27% by days 5 and 8 postovariectomy (p < 0.01) and continued to decrease up to day 50 postovariectomy (p < 0.01). The trabecular bone volume decreased 25% by 8 days postovariectomy (p < 0.01), and it continued to decrease through day 50. DPD cross-link excretion had increased 37% on day 13 (p < 0.01) and by over 100% of baseline by day 50 postovariectomy. Trabecular bone connectivity and volume deteriorate rapidly while DPD cross-link excretion increased more slowly in acute estrogen deficiency. These data suggest that if an agent is to preserve fully trabecular bone structure, it must be instituted very early in the estrogen-deficient state. They also suggest that a lag time exists before DPD excretion properly mirrors newly induced conditions of high bone turnover in this rat model.

Linkage of a gene causing high bone mass to human chromosome 11 (11q12-13)

The purpose of this paper is to report the linkage of a genetic locus (designated "HBM") in the human genome to a phenotype of very high spinal bone density, using a single extended pedigree. We measured spinal bone-mineral density, spinal Z(BMD), and collected blood from 22 members of this kindred. DNA was genotyped on an Applied Biosystems model 377 (ABI PRISM Linkage Mapping Sets; Perkin Elmer Applied Biosystems), by use of fluorescence-based marker sets that included 345 markers. Both two-point and multipoint linkage analyses were performed, by use of affected/unaffected and quantitative-trait models. Spinal Z(BMD) for affected individuals (N = 12) of the kindred was 5.54 +/- 1.40; and for unaffected individuals (N = 16) it was 0.41 +/- 0.81. The trait was present in affected individuals 18-86 years of age, suggesting that HBM influences peak bone mass. The only region of linkage was to a series of markers on chromosome 11 (11q12-13). The highest LOD score (5.21) obtained in two-point analysis, when a quantitative-trait model was used, was at D11S987. Multipoint analysis using a quantitative-trait model confirmed the linkage, with a LOD score of 5.74 near marker D11S987. HBM demonstrates the utility of spinal Z(BMD) as a quantitative bone phenotype that can be used for linkage analysis. Osteoporosis pseudoglioma syndrome also has been mapped to this region of chromosome 11. Identification of the causal gene for both traits will be required for determination of whether a single gene with different alleles that determine a wide range of peak bone densities exists in this region.

Prostaglandin E2 increases the skeletal response to mechanical loading

The study tested the influence of prostaglandin E2 (PGE2) on the skeletal response to increased in vivo mechanical loading through a four-point bending device. One hundred and twenty Sprague-Dawley female rats (6 months old, 354 +/- 34 g) were divided into 12 groups to accommodate all possible combinations of doses of loads (25, 30, or 35 N) and PGE2 (0, 0.1, 0.3, or 1 mg/kg). Rats received subcutaneous injections of PGE2 daily and in vivo loading of the right tibia every Monday, Wednesday, and Friday for four weeks. Histomorphometric analysis of the periosteal and endocortical surfaces following in vivo dual fluorochrome labeling was performed on both the loaded region of the right tibial diaphysis and a similar region of the left tibial diaphysis. Without PGE2, the threshold for loading to stimulate bone formation was 30 N (peak strain 1360 mu epsilon) at the periosteal surface and 25 N (peak strain 580 mu epsilon) at the endocortical surface. Without loading, the minimum dose of PGE2 to stimulate bone formation at all surfaces was 1 mg/kg/day. When 1 mg/kg/day PGE2 was combined with the minimum effective load, an additive effect of PGE2 and loading on bone formation was observed at the endocortical surface, but a synergistic effect was noted at the periosteal surface. No combined effect of ineffective doses of loading and PGE2 was found. A synergistic effect at peak strains of approximately 1625 mu epsilon on the periosteal surface could suggest either the involvement of locally produced growth factors or autoregulation of endogenous synthesis of PGE2 by exogenously administered PGE2.

Dose-response relationships for alendronate treatment in osteoporotic elderly women. Alendronate Elderly Osteoporosis Study Centers

Alendronate (ALN) is an aminobisphosphonate employed as an antiresorptive agent in the treatment of osteoporosis. The present study was carried out to determine dose-response relationships, particularly the effects of relatively low doses of ALN, on bone mineral density (BMD), biochemical indexes of bone and mineral metabolism, and bone histology, with particular attention to effects in elderly women. This prospective, randomized, double blind, 2-yr multicenter study compared the effects of placebo with those of 1.0, 2.5, or 5.0 mg ALN daily. All subjects received supplemental calcium (500 mg daily) as the carbonate. We studied 359 women with lumbar spine BMD at least 2.0 SD below the peak young adult mean. Subjects were stratified by age, with 135 aged 60-69 yr and 224 aged 70-85 yr. Histomorphometry was performed on transiliac bone biopsies obtained from 104 subjects after 1 yr and from 83 subjects after 2 yr. This study elucidated the previously uninvestigated lower region of the dose-response curve for ALN in osteoporosis. Over 2 yr, treatment with 1.0, 2.5, or 5.0 mg/day increased lumbar spine BMD, on the average, by 0.65%, 3.54%, and 5.67%, respectively, compared with that in the placebo group (P < 0.001 vs. placebo for the 2.5 and 5 mg groups). Significant dose-related increases were also seen in BMD at appendicular sites and in total body BMD. Dose-dependent reductions in bone turnover to new steady states were indicated by serum and urine biochemical markers as well as by histomorphometry. There was also a dose-related reduction in the proportion of subjects suffering nonvertebral fractures (P < 0.05). Safety profiles were similar for the ALN and placebo groups and for both age strata. Efficacy was similar for both age strata. There was no evidence of impaired mineralization or other histological abnormalities due to ALN treatment. We conclude that treatment with ALN over a period of 2 yr was well tolerated and produced dose-dependent increases in BMD without evidence of a plateau over the dose range of 1.0-5.0 mg daily. One milligram daily did not result in a significant effect on BMD, and 5.0 mg daily produced favorable effects at all sites measured. Other studies have demonstrated somewhat greater effects on 10 mg daily. ALN, was equally effective and well tolerated in osteoporotic women over 70 yr old as in younger women with the same condition.

Correcting calcium nutritional deficiency prevents spine fractures in elderly women

We tested the spine antifracture and bone sparing efficacy of 1.2 g/day of oral calcium as carbonate in two groups of elderly women, one with prevalent fractures (PF, n = 94) on entry and the other without (NPF, n = 103). It was a prospective randomized, double-blind, placebo-controlled trial in mostly rural communities in women over age 60 who were living independently and were consuming < 1 g/day of calcium. We obtained annual lateral spine radiographs and semiannual forearm bone density over 4.3 +/- 1.1 years and determined vertebral fractures by radiographic morphometry augmented by physician assessment. In the PF group, 15 of 53 subjects on calcium had incident fractures, compared with 21 of 41 on placebo (p = 0.023, chi2). Calcium did not reduce the rate of incident fractures in the NPF group. Those with a prevalent fracture on entry and not treated with calcium were 2.8 times more likely to experience an incident fracture than all others. Change in the forearm bone mass on placebo in the PF group was -1.24 +/- 2.41%/year compared with +0.31 +/- 1.80%/year on calcium (p < 0.001). In the NPF group, the difference was less: -0.39 +/- 2.08%/year versus 0.00 +/- 1.64%/year (p = 0.2). We conclude that in elderly postmenopausal women with spine fractures and selfselected calcium intakes of < 1 g/day, a calcium supplement of 1.2 g/day reduces the incidence of spine fractures and halts measurable bone loss.

RS-66271, a C-terminally substituted analog of human parathyroid hormone-related protein (1-34), increases trabecular and cortical bone in ovariectomized, osteopenic rats

It was predicted from the amino acid sequence of the bone anabolic peptides, parathyroid hormone (PTH) (1-34) and PTH related protein (PTHrP) (1-34), that the C-terminal amino acids form an amphipathic alpha-helix. Therefore, we substituted a model amphipathic alpha-helical peptide (MAP) sequence in the C-terminal region of hPTHrP(1-34), obtaining RS-66271 ([MAP1-10]22-31 hPTHrP(1-34)-NH2). The anabolic activities of RS-66271 and hPTHrP(1-34) were evaluated in 3-month-old, ovariectomized (OVX) osteopenic rats. Subcutaneous injection of hPTHrP(1-34) at 80 micrograms/kg/day partially reversed estrogen depletion trabecular bone loss but was ineffective in the cortex. In contrast, RS-66271 dose-relatedly reversed loss at both sites and, at 80 micrograms/kg/day, returned both trabecular and cortical bone calcium to the level of sham-operated controls. Histomorphometric analysis showed significantly elevated bone formation rates over vehicle-treated OVX in both trabecular and cortical tibial bone following treatment with RS-66271. Electron microscopy showed an increase in the relative surface area of vertebral trabeculae covered by osteoblasts in animals treated with RS-66271. These studies demonstrate that the C-terminal amino acids of hPTHrP(1-34) can be replaced by a model amphipathic helix and that the new chemical entity has greater anabolic activity than the parent peptide. The results suggest that RS-66271 may be a candidate molecule for the treatment of human osteoporosis.

Bone mineral density and turnover following forelimb immobilization and recovery in young adult dogs

The purpose of this experiment was to study changes in bone mass, structure, and turnover in the canine forelimb after unilateral immobilization and recovery. The right forelimbs of 14 adult mongrel dogs were immobilized for 16 weeks. Six dogs served as controls. Seven immobilized and three control dogs were euthanized at the end of the immobilization period. Recovery consisted of 16 weeks of kennel confinement followed by 16 weeks of treadmill exercise. Seven once-immobilized and three control dogs were euthanized at the end of the recovery period. Bone mineral density of both the proximal (PBMD) and central (CBMD) radius was determined by dual X-ray absorptiometry. Standard histomorphometric endpoints for bone mass and turnover were determined in the cancellous bone of the proximal radius. After immobilization, PBMD, CBMD, and trabecular thickness were lower in the immobilized limb than in either the contralateral or control limbs (P < 0.05). Only CBMD remained significantly lower (P < 0.05) after recovery. At the end of immobilization, bone formation endpoints were significantly higher in the immobilized limb than both the contralateral and control limbs. Bone turnover was also significantly lower in the contralateral limb than in the immobilized and control limbs. After recovery, all differences in bone turnover had resolved. Immobilization of 16 weeks duration caused an elevation in cancellous bone formation rate and reduced bone density in both cortical and cancellous bone. After 32 weeks of recovery, turnover abnormalities disappeared, cancellous bone normalized, but cortical bone mass remained low. Recovery of cortical bone from immobilization takes longer than recovery of cancellous bone.

Long-term low ascorbic acid intake reduces bone mass in guinea pigs

The effect of long-term (1 y) low to excess ascorbic acid (AA) intake on bone mass was evaluated using guinea pigs that were 12-14 d old at the start of the experiment. Dietary AA was low (0.15 g/ kg diet) (n = 7), normal (0.50 g/kg) (n = 8) or excess (10 g/kg) (n = 8). After 12 mo, total body bone mineral density (BMD, mg/cm2) and bone mineral content (BMC, g) were determined by dual energy X-ray absorptiometry. Histomorphometric analysis of the cancellous bone of the proximal tibial metaphysis was completed after in vivo dual fluorochrome labeling. Total body BMD of the low AA group was 4.9% lower (P < 0.05), and total body BMC was 12.4% lower (P < 0.05) than in the normal AA group. Total body BMD and BMC were similar in normal and excess AA groups and in the low and excess AA groups. Histomorphometric analysis indicated significantly greater (P < 0.05) double-labeled bone surface, mineralizing surface, and bone formation rate in the low AA guinea pigs compared with the normal AA animals. Thus, there was greater bone turnover in the low AA group than in the normal AA guinea pigs. No differences in histomorphometric endpoints existed between the normal AA and excess AA groups. Long-term AA deficiency, during the period of rapid growth and slower phases of skeletal maturation, resulted in bone abnormalities in adult guinea pig skeletons. Long-term dietary AA excess caused no such abnormalities.

Bone-selective analogs of human PTH(1-34) increase bone formation in an ovariectomized rat model

Intermittent parathyroid hormone (PTH) therapy increases bone mass. The purpose of this study was to determine if analogs of human PTH(1-34) (hPTH[1-34]), which differ from the native sequence in their receptor-activating properties, could promote bone formation in an ovariectomized (OVX) osteopenic rat model. We synthesized two hPTH(1-34) analogs with single substitutions for serine in the 3-position that in vitro are partial agonists in kidney. In the renal cell line OK, maximal cyclic adenosine monophosphate (cAMP) activation by [His(3)]hPTH(134) was 50%, and maximal cAMP activation by [Leu(3)]hPTH(1-34) was 20% of that produced by hPTH(1-34). Both analogs were full agonists in UMR-106 rat osteosarcoma cells and other bone-derived systems, but both had reduced potency compared with hPTh(1-34). Six-month-old retired breeder Sprague-Dawley rats were ovariectomized, and five animals underwent sham operation. On day 56 post-OVX, five sham-operated and five pre-PTH treatment OVX animals were sacrificed, and the remaining animals were randomized into 10 groups of six animals each. All other animals were injected with one of the hPTH analogs or hPTH(1-34) at 0, 4, 40, or 400 mu g/kg of body weight (BW)/day and were killed on day 84. Histomorphometry of the proximal tibia metaphysis and biochemical markers of bone turnover (osteocalcin and pyridinoline cross-links) were the primary endpoints. The cancellous bone volume was significantly lower at day 56 post-OVX (pretreatment) and at day 84 post-OVX (post-vehicle treatment) than at baseline. None of the compounds significantly increased the cancellous bone volume. Trabecular number declined after OVX and did not change with hPTH treatment. In contrast, the trabecular thickness declined after OVX but was higher after treatment with 40 mu g/kg of BW/day or 400 mu g/kg of BW/day of hPTH(1-34). In OVX rats, the mineralizing surface was higher than baseline at day 56 and fell toward control levels by day 84. All three peptides produced marked dose-related increases in the mineralizing surface and bone formation rates, but the two analogs were less potent than hPTH(1-34). Likewise, all peptides produced significant dose-related increases in the serum osteocalcin level. The osteoclast surface was not affected by OVX but was decreased with medium and high doses of hPTH(1-34). Pyridinoline cross-link excretion was not significantly affected by treatment with hPTH(1-34) but responded with a dose-dependent decrease to treatment with [His3]hPTH(1-34). These data suggest that bone selective analogs of hPTH(1-34) maintain the ability to induce bone formation but are less potent than hPTH(1-34).

Scurvy results in decreased collagen synthesis and bone density in the guinea pig animal model

The effect of severe ascorbic acid deficiency on bone remodeling and collagen synthesis was evaluated in a 21 day experiment, using the scorbutic guinea pig model. Animals (n = 6-7/group) were assigned to one of three groups: scorbutic, pair-fed ascorbic acid-replete, or ad libitum ascorbic acid-replete groups. After 2 weeks, scorbutic animals started voluntarily decreasing food intake and losing weight. By day 19-21, at which time bone and tissue samples were collected and analyzed, scorbutic animals decreased food intake to 46% of usual and lost 9% body weight. Serum 25OHD3, 1,25(OH)2D3, calcium, and albumin were significantly lower (p < 0.05) in the scorbutic animals than in the other groups. Bone mineral density and bone mineral content of the proximal and central femur were significantly lower in the scorbutic group than in the other groups (p < 0.05). Morphometric analysis of tibia indicated significantly lower bone volume, fewer and thinner trabeculae, and a thinner growth plate in the scorbutic group, compared to the pair-fed and ad libitum groups (p < 0.05). Osteoclast surface was about 60% higher in the scorbutic group than in the pair-fed and ad libitum control groups (0.05 < p < 0.10). Mechanical strength of the femur and lumbar vertebral body tended to be lower when bone mass was altered in the same group. Collagen synthesis of articular cartilage and tendons was lower in the scorbutic group than in the pair-fed or ad libitum groups (p < 0.05). In conclusion, scurvy but not food restriction, per se, results in alterations in bone mass and tissue collagen synthesis.

Functional characterization of prostaglandin E2 inducible osteogenic colony forming units in cultures of cells isolated from the neonatal rat calvarium

Prostaglandin E2 (PGE2) increases the number of mineralized nodules that form in cultures of rat calvarial (RC) cells. The purpose of our study was to characterize PGE2-inducible osteogenic colony forming units (CFU-Os) by determining their number, the cell populations from which they were released, their specific responsive period to PGE2, and their proliferating and differentiating characteristics under the stimulation of PGE2. Limiting dilution analysis was used to determine the number of PGE2-inducible CFU-Os. Sequential digestion of intact rat parietal bones with collagenase isolated 5 subpopulations of RC cells that were used to estimate the cell populations where PGE2-inducible CFU-Os resided. The responsive period of PGE2-inducible CFU-Os to PGE2 was evaluated by treating cultures of mixed RC cells for all possible combinations of days 1-10, 11-20, and 21-30. PGE2 effects on proliferation and differentiation of CFU-Os were evaluated by comparing the DNA synthesis and AP activity in subpopulations I and IV on days 3, 6, and 9. Results showed: (1) PGE2-inducible CFU-Os represent 0.27% of cells in the mixed RC population, (2) the majority of determined and PGE2-inducible CFU-Os were found in the subpopulations released during the 60-100 min digestion periods, (3) the response of PGE2-inducible CFU-Os is limited to the first 10 days of culture, and (4) PGE2-stimulated nodule formation is associated with an early increase in DNA synthesis and a sustained increase in alkaline phosphatase activity. We conclude that, functionally, PGE2-inducible CFU-Os are slowly proliferating AP negative cells primarily found in the subpopulations III-V. PGE2 stimulates them to proliferate and become AP+, and function as determined CFU-Os to form mineralized nodules in vitro.

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.

Mechanical loading stimulates rapid changes in periosteal gene expression

Although mechanical forces regulate bone mass and morphology, little is known about the signals involved in that regulation. External force application increases periosteal bone formation by increasing surface activation and formation rate. In this study, the early tibial periosteal response to external loads was compared between loaded and nonloaded contralateral tibia by examining the results of blot hybridization analyses of total RNA. To study the impact of external load on gene expression, RNA blots were sequentially hybridized to cDNAs encoding the protooncogene c-fos, cytoskeletal protein beta-actin, bone matrix proteins alkaline phosphatase (ALP), osteopontin (Op), and osteocalcin (Oc), and growth factors insulin-like growth factor I (IGF-I) and transforming growth factor-beta (TGF-beta). The rapid yet transient increase in levels of c-fos mRNA seen within 2 hours after load application indirectly suggests that the initial periosteal response to mechanical loading is cell proliferation. This is also supported by the concomitant decline in levels of mRNAs encoding bone matrix proteins ALP, Op, and Oc, which are typically produced by mature osteoblasts. Another early periosteal response to mechanical load appeared to be the rapid induction of growth factor synthesis as TGF-beta and IGF-I mRNA levels were increased in the loaded limb with peak levels being observed 4 hours after loading. These data indicate that the acute periosteal response to external mechanical loading was a change in the pattern of gene expression which may signal cell proliferation. The altered pattern of gene expression observed in the present study supports previous evidence of increased periosteal cell proliferation seen both in vivo and in vitro following mechanical loading.

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)

Effects of recombinant human interleukin-6 administration on bone in rhesus monkeys

The role of interleukin-6 in the bone microenvironment is controversial. We studied the effect of recombinant human interleukin-6 (rhIL-6) administration on bone metabolism in 10 adult female rhesus monkeys (age 12-27 years). Monkeys received rhIL-6 (15 micrograms/kg/day) daily by subcutaneous injection for 28 days. Serum alkaline phosphatase, osteocalcin, and 24 h urinary calcium excretion were determined before, during (at weeks 2 and 4), and after (at week 6) treatment. Transilial biopsies (right and left) were obtained before treatment was initiated and just after the final (28th) dose at week 4. The serum alkaline phosphatase significantly increased at 2 and 4 weeks of rhIL-6 administration. Osteocalcin and urinary calcium excretion significantly decreased at week 2. Upon treatment with rhIL-6 significant reductions in OS/BS and Ob.S/BS were observed without changes in other static histomorphometry parameters. The reductions in urinary calcium excretion, serum osteocalcin, and the static bone parameters are consistent with an IL-6 induced reduction in bone formation or turnover. Whether this pharmacologic effect is relevant at the physiologic level remains to be determined.

Periosteal bone formation stimulated by externally induced bending strains

The rat tibia four-point bending model is a new mechanical loading model in which force is applied through external pads to the rat lower limb. The advantages of the model are controlled force application to a well-defined bone, noninvasive external loading, and the addition of loads to normal daily activity. A disadvantage of the model is that the pads create local pressure on the leg at the contact sites. This study examined the differences in tibial response to bending strains and to local pressure under the pads. A total of 30 adult Sprague-Dawley rats were randomized into three external loading groups: bending, cyclic pressure, and static pressure. The right leg of each rat was externally loaded to create either bending or local pressure without bending; the left leg served as a control. Strains on the lateral surface averaged 1200 mu epsilon in compression during bending load application and < 200 mu epsilon in compression during pressure loading. Histomorphometric data were collected from three regions: the maximal bending region, under the loading pads, and outside the maximal bending region. In the maximal bending region, bending loads created greater mineral apposition rate (MAR) on the lateral surface and greater MAR and formation surface on the medial surface of loaded than control tibiae. The region under the bending pad was exposed to similar bending strains and showed the same pattern of increased MAR as sections from the maximal bending region. Cyclic pressure had no effect on periosteal MAR or formation surface. Static pressure increased MAR only on the lateral tibial surface. Bending stimulates bone formation in regions with the highest bending strains. Similar forces applied only in the form of pressure loading do not stimulate tibial formation either at the contact site or between loading pads. These results suggest that externally applied forces of moderate magnitude stimulate bone formation primarily as a result of increased bending strains, not local pressure at the contact site.

Current and investigational approaches for reversing established osteoporosis

Osteoporosis is a disease of elderly women marked by low bone mass and increased risk of fracture. Though its prevalence can be reduced by timely estrogen replacement at menopause, many persons present with fragility fractures long after much bone has been lost. Osteoporotic subjects have low bone mass and poor structure but few or no metabolic abnormalities, such as ongoing bone loss, for treatment to normalize. The problem is to increase their bone mass and improve their bone structure. Today's major therapeutic approaches are summarized in Table 2. Ironically, they aim at stopping bone loss. Although preventing the skeleton of an osteoporotic person from growing weaker by stopping bone loss is better than allowing the process to continue, raising her to a significantly higher level of bone mass would be a better aim. Existing agents that stop bone loss by reducing turnover also increase bone mass mildly by filling the remodeling space. The result is a rise in bone mass during the first year or two of treatment to a new steady state 2% to 5% higher than baseline that persists throughout treatment. Fluoride increases spinal bone mass markedly. It decreases vertebral, but not hip fractures, but is associated with side effects and a nonresponse rate that makes pursuing other therapies attractive. Agents that upregulate bone mass through regulatory means have been tested in preclinical and a few clinical trials. PGE2 has been thoroughly tested preclinically. By studying PGE2, the field has learned that marked bone mass increases in the estrogen-deplete osteopenic skeleton are possible. The lack of bone specificity for PGE2 will probably limit its use to that of preclinical demonstration agent but leave open the possibility that less potent members of the prostaglandin family with better bone specificity might have promise as osteoporosis treatments. PTH or one of its analogues shows good promise for osteoporosis treatment. The wide availability of cheap PTH or proprietary analogues with similar activity will do much to speed its development. It increases bone formation and cancellous bone mass markedly. If PTH increases bone mass consistently in either large animal or human trials while causing only mild transient cortical bone mass declines, it can be a successful osteoporosis treatment agent. Bone growth factors appear to have much untapped potential for furthering the understanding of local control of bone processes and possibly for treating osteoporosis. Another possibility is biphasic therapy.(ABSTRACT TRUNCATED AT 400 WORDS)

Cancellous bone behavior in hindlimb immobilized rats during and after naproxen treatment

Temporary immobilization creates bone loss. The purpose of this investigation was to use an agent to protect the skeleton from bone loss bone during temporary immobilization. Eighty-nine 6-month-old retired breeder Sprague-Dawley female rats were used. Animals were randomly divided into six groups of equal numbers. Four groups were given drinking water from day 0, containing naproxen (100 or 200 mg/l). At day 7, half the animals in all groups had their right hindlimb immobilized. At day 49, half the immobilized rats and non-immobilized controls were sacrificed. The remaining rats were remobilized and the drug was stopped. At day 91, all remaining rats were sacrificed. Gastrocnemius and soleus muscle weights were determined. Right tibiae were analyzed for cancellous bone mass, bone structural and bone dynamic variables. At the close of immobilization, bone mass was lower in the right (immobilized) hindlimb of the immobilized group than in the non-immobilized group. Immobilized rats drinking 100 mg/l naproxen water had significantly higher bone mass in their immobilized limbs than did untreated immobilized rats, but all rats drinking 200 mg/l naproxen water had lower bone mass than controls. After 6 weeks of recovery, bone mass in the immobilized limb of untreated formerly immobilized rats improved, but remained below untreated never-immobilized rats. Formerly immobilized rats that had been treated with 100 mg/l naproxen water had normal bone mass after 6 weeks of recovery. Naproxen, an agent that mildly depresses activation frequency, prevents some of the transient bone mass and structural deterioration during temporary immobilization. Such treatment facilitates a more rapid return to normal bone mass, though not to normal structure. The more rapid recovery occurs because the difference from normal is less, not because of more rapid formation in recovering animals.

Bone response to alternate-day mechanical loading of the rat tibia

Mechanical loading of the living skeleton influences bone formation, mass, and strength. The primary purpose of the present study was to examine the influence of different loading schedules (days/week) on the bone response to external loading using an in vivo rat tibia four-point bending model. Three studies were conducted to (1) characterize the loaded region, (2) examine the variation of the response within the loaded region, and (3) test the response to different loading schedules. In all studies adult female retired breeder Sprague-Dawley rats were used (6 months, 285 g). First, the location of the loaded region during four-point bending was determined by radiogrammetry of 7 rats. Second, 5 rats were externally loaded for 8 of 10 days at 31 N, 36 cycles, and 2 Hz (1349 +/- 244 mu epsilon). The extent of labeled (forming) periosteal and endocortical surface in the loaded region was compared both among four serial sections from the same tibia and between the loaded and the contralateral tibiae. Finally, 50 rats were randomized into five groups: two nonloaded, control and sham, and three loaded, alternate day, Monday, Wednesday, and Friday, and daily. The rats were externally loaded for 3 weeks at 35 N, 36 cycles, and 2 Hz (1533 +/- 308 mu epsilon). The tibia and fibula were studied for labeled surfaces and mineral apposition rate. For adult female rats with tibial length 39 mm, the loaded region was located 3.5-14 (+/- 0.7) mm proximal to the tibia-fibula junction (TFJ).(ABSTRACT TRUNCATED AT 250 WORDS)

A paradigm for skeletal strength homeostasis

This article integrates engineering principles with skeletal biology to describe skeletal strength homeostasis. Skeletal strength revolves around its perceived mechanical usage. Mass, geometric properties, and fatigue damage burden are the principle determinants of structural strength. Bone cells form sensor and effector systems that monitor usage and adjust strength and stiffness by changing mass, geometric properties, and fatigue damage burden. The bone lining cell-osteocyte complex is the sensor; the bone modeling and remodeling systems are the effectors. Deformation and fatigue damage in bone are the signals received by the sensor. Accumulated energy in the sensor's cytoskeleton determines the rate at which the sensor sends messages to the effectors. The activity of both effector systems is proportional to the rate of incoming messages. Modeling raises bone strength and stiffness by improving geometric properties as it adds bone where customary deformation is greatest. Remodeling improves bone strength by replacing fatigue-damaged areas without mass changes. Bone removed during modeling and remodeling comes from sites where the impact on bone strength and stiffness is least. Hormones and agents alter the rigidity of the cytoskeleton and, thus, its capacity to deform and store energy. Osteopenic agents make it more rigid, causing detection of fewer deformations and transmission of fewer loading signals to the effector. Osteotropic agents decrease the rigidity of the cytoskeleton, causing detection of more strain events and transmission of more loading signals to the effector. Agent treatment thus establishes false conditions of disuse or hyperuse.

Precision and accuracy for rat whole body and femur bone mineral determination with dual X-ray absorptiometry

Precision and accuracy for rat whole body and excised femur bone mineral density (BMD) measurements were evaluated with two dual X-ray absorptiometry (DXA) systems. The 'small subject' mode on the Norland XR-26 (XR), and the 'ultra high resolution mode' on the Hologic QDR-1000/W(QDR) were used for the analysis. The whole body mode was only available on the XR. The lowest precision error for the whole body was found using a scan resolution of 1.0 x 1.0 mm and a scan speed of 15 mm/s. The scan spatial resolution of the femur measurement was approximately eight times higher on the QDR than on the XR. However, the XR allowed analysis of an arbitrary region of interest within the femur, which was not easily done with the QDR. Precision for the total femur measurement on the QDR (0.5-0.9%) was approximately two to four times superior to that of the XR (1.5-4.3%). The difference may be due to the superior scan resolution of the QDR. Bone mineral content and BMD on the QDR significantly declined with an increase of water depth (P < 0.001). No significant change was observed on the XR. Both DXA systems demonstrated an excellent correlation (r > or = 0.98) with ash weight under the scan conditions examined. The optimal scan condition for the excised femur measurement on the XR was obtained with 1.5-2.5 cm of perspex or water and a scan speed of 10 mm/s. For the QDR, we recommend scanning the rat femur with approximately 2.5 cm of perspex or water in terms of precision and accuracy.

The health care status of the diabetic population as reflected by physician claims to a major insurer

BACKGROUND

Conventional epidemiologic data suggest that diabetic patients use more health care resources than nondiabetic patients, yet overall health care use by diabetic individuals has never been fully quantitated. We took a new approach to this issue based on the actual economics of the provision of health care to diabetic insured individuals.

METHODS

The claims records in the Mutual of Omaha Current Trends database, which contains information on more than 400,000 individuals, were surveyed to identify patients with diabetes and create the contrast population of nondiabetic patients by exclusion. International Classification of Diseases, Ninth Revision, Clinical Modification, codes and Physicians' Current Procedural Terminology, Fourth Edition, codes were used to determine all diagnoses recorded and all physician services rendered to the contrast populations. Age- and sex-adjusted comparisons were performed using Mantel-Haenszel procedures to determine an adjusted odds ratio (AOR).

RESULTS

A total of 13,304 diabetic individuals and 388,053 nondiabetic individuals who received health care services from January 1, 1988, to January 1, 1989, were identified. Diabetic insured individuals constituted 3.1% of the overall insured population yet accounted for 8.3% of the charges (P < .01). Inpatient charges accounted for 81% of total diabetic charges but only 61.5% of total nondiabetic charges (P < .001). Diabetic insured individuals had twice as many physician office visits (AOR = 1.87; 95% confidence interval [CI], 1.79 to 1.96), with 2.5 times more physician hospital visits [AOR = 2.50; 95% CI, 2.27 to 2.75). However, the increases in physician care were not uniformly distributed across the diagnostic spectrum. The frequencies of well-established complications of diabetes, such as ischemic heart disease (AOR = 3.32; 95% CI, 3.12 to 3.53), peripheral vascular disease (AOR = 3.14; 95% CI, 2.79 to 3.53), and eye disease (AOR = 3.10; 95% CI, 2.94 to 3.27), were threefold higher in the diabetic group, with parallel increases in related medical services, such as cardiac catheterization (AOR = 3.02; 95% CI, 2.27 to 4.0), vascular surgery (AOR = 2.94; 95% CI, 2.64 to 3.27), and ophthalmologic procedures (AOR = 2.94; 95% CI, 2.72 to 3.18). In contrast, most diagnostic categories showed little or no increase. For example, the frequency of neoplasms (AOR = 1.11; 95% CI, 1.03 to 1.19) was minimally increased, and the associated procedural concomitants of therapeutic radiology (AOR = 0.81; 95% CI, 0.47 to 1.39) and chemotherapy (AOR = 0.98; 95% CI, 0.60 to 1.60) were not increased in the diabetic group.

CONCLUSIONS

Our most important new finding is that diabetic patients have neither an elevated risk for a wide spectrum of diseases nor an increase in the receipt of physician services for diagnostic categories without increased risk, despite more frequent physician encounters. We provide real-world risk estimates that help in calculating the effect of offering specific insurance to diabetic individuals or including them in group health plans. The techniques we have developed to analyze computerized claims databases in this way may serve to better quantify the true impact of chronic diseases on the health care system.

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)

The effect of recombinant human (1-84) or synthetic human (1-34) parathyroid hormone on the skeleton of adult osteopenic ovariectomized rats

The purpose of this study was to evaluate the dose-effect relationship of recombinant human PTH [hPTH-(1-84)] and synthetic human PTH [sPTH-(1-34)] for the skeleton of estrogen-deplete osteopenic rats. Ex vivo densitometry of regionalized whole femurs and histomorphometry of proximal tibial cancellous bone were the end points. Retired breeder female rats, aged 6-7 months, were used. Ten were killed at baseline, and the rest were ovariectomized (OVX). On day 42, a pre-PTH treatment OVX group was killed. The rest were then treated by daily sc injection with hPTH (0, 1.55, 15.5, or 155 micrograms/kg BW.day) or sPTH (0.55, 5.5, or 55 micrograms/kg BW.day) and killed on day 70. The level of cancellous bone mineral was lower in pretreatment OVX rats than at baseline. It was higher in rats treated with 15.5-155 micrograms/kg.day hPTH and 5.5-55 micrograms/kg.day sPTH than in pretreatment and vehicle-treated OVX rats. Cancellous bone volume was also lower both 42 and 70 days after OVX. Although hPTH did not affect cancellous bone volume, treatment with 5.5-55 micrograms/kg.day sPTH caused higher bone volume than in either pretreatment or vehicle-treated OVX rats. Trabecular number declined after OVX and did not change with PTH treatment. In contrast, trabecular thickness declined after OVX, but was higher after 15.5-155 micrograms/kg.day hPTH and 5.5-55 micrograms/kg.day sPTH treatment. In OVX rats, the amount of mineralizing surface was greater by day 42 and fell toward control levels by day 70. It was greater in rats treated with 15.5-155 micrograms/kg.day hPTH or 5.5-55 micrograms/kg.day sPTH than in vehicle-treated OVX rats. On a molar basis, sPTH was modestly more potent than hPTH. Osteoclast surface was not affected by PTH treatment. Treating estrogen-deplete osteopenic adult rats for 28 days with 15.5-155 micrograms/kg.day hPTH or 5.5-55 micrograms/kg.day sPTH increases trabecular thickness, but not trabecular number, to cause a rise in bone mass. The extent of mineralizing surface rises without a change in resorption surface. The marked rise in mineralizing surfaces suggests that extended in vivo treatment with PTH activates osteogenic precursor cells near once quiescent surfaces to become osteoblasts.

Effect of ovariectomy on bone response to in vivo external loading

This study was undertaken to find whether the bone response to increased external loading (EL) of the tibia in rats is affected by estrogen depletion. Female Sprague-Dawley rats 6 months were randomly assigned to four groups of 10 each: sham ovariectomy without loading (Shm-XL), ovariectomy without loading (OVX-XL), sham ovariectomy with external loading (Shm-EL), and ovariectomy with external loading (OVX-EL). In vivo external loading by a four-point bending device was initiated 4 weeks after surgery. The right lower leg of each EL rat was loaded at 31.4 +/- 0.2 N for 36 cycles at 2 Hz every other day for 21 days (11 loading days). Mean in vivo induced strain was 1305 microstrain (mu epsilon) for Shm-EL rats and 1280 mu epsilon for OVX-EL rats. With external loading of the tibia, periosteal bone formation rose equally in Shm and OVX rats. Woven bone was present around the tibia or fibula in 60% of the loaded rats and none of the control rats. No loading response occurred either at the endocortical surface or in the cancellous bone of the proximal tibial metaphysis. After OVX, cancellous bone area in the proximal metaphysis declined and formation surface rose compared to Shm rats. Although periosteal and endocortical bone formation rose after OVX, no cortical bone loss occurred. We conclude that ovariectomy and attendant loss of endogenous estrogen do not change the cortical bone response to an external load of about 1300 mu epsilon in rats. However, these results may not predict the cortical bone response to loading in animals with Haversian remodeling that display estrogen-related loss of cortical bone.