Biomedical subjects

D B Kimmel

Publications and source records attributed to D B Kimmel.

At least 19 recordsLinked to original sources

PubMed2001

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.

Animals↗

PubMed2001

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.

Animals↗

PubMed2001

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.

Animals↗

PubMed2001

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.

Animals↗

PubMed2000

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.

Absorptiometry, Photon↗

PubMed1999

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.

Animals↗

PubMed1999

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.

Bone Density↗

PubMed1999

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.

Animals↗

PubMed1998

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.

Analysis of Variance↗

PubMed1998

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.

Alkaline Phosphatase↗

PubMed1998

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.

Animals↗

PubMed1998

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.

Amino Acids↗

PubMed1997

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.

Absorptiometry, Photon↗

PubMed1997

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.

Aged↗

PubMed1997

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.

Animals↗

PubMed1996

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.

Alkaline Phosphatase↗

PubMed1996

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).

Animals↗

PubMed1996

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.

Amino Acid Sequence↗